Q.Show by a chemical reaction with water that $Na_2O$ is a basic oxide and $Cl_2O_7$ is an acidic oxide.

Showing the 12 most recent of 41 on this concept.

1. AP EAPCET 2026Set eng-2026-05-12-AN1 markMCQ
   Q.The oxide and hydroxide of which metal are amphoteric in nature? (A) Li (B) Na (C) Mg (D) Be

   ›Reveal solutionSolution

   This tests the diagonal relationship in the periodic table; only beryllium among these s-block metals has an amphoteric oxide/hydroxide.

   Concept and Intuition

   The first member of a group in the s- and p-blocks often resembles the element diagonally below-right more than its own heavier group members, due to similar charge/size ratios (polarising power). Be (small, highly charged for its size) behaves like $Al^{3+}$, whose oxide and hydroxide are famously amphoteric. The rest of group 1 (Li, Na) and the heavier group 2 metals (Mg, Ca, ...) form purely basic oxides/hydroxides.

   Step-by-Step Solution

   1. Li: $Li_2O$ and $LiOH$ are basic (mildly, due to Li's small size, but not amphoteric).
   2. Na: $Na_2O$ and $NaOH$ are strongly basic.
   3. Mg: $MgO$ and $Mg(OH)_2$ are basic. …

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2. AP EAPCET 2026Set eng-2026-05-12-AN1 markMCQ
   Q.Observe the following statements about the oxides of group 14 elements I. $CO_2$ is an acidic oxide but $CO$ is a neutral oxide II. Cristobalite is the crystalline form of silica III. Liquid $CO$ is called dry ice IV. Both $CO$ and $CO_2$ act as Lewis acids The correct statements are (A) I & II only (B) I & III only (C) I & IV only (D) III & IV only

   ›Reveal solutionSolution

   Checking each statement about group-14 oxides: I and II are textbook-correct; III confuses dry ice (solid $CO_2$) with liquid CO; IV wrongly calls CO a Lewis acid when it is a Lewis base. So only I & II are correct.

   Concept and Intuition

   Acidic/basic/neutral character of oxides and the crystalline forms of silica are standard NCERT facts about group 14. Lewis acid/base character depends on whether a species donates or accepts an electron pair — $CO$'s carbon end has a lone pair it donates to metals (forming metal carbonyls like $Ni(CO)_4$), making it a Lewis base, while $CO_2$'s central carbon is electron-deficient enough to accept a nucleophile (e.g. $OH^-$ in the formation of carbonate), making it a Lewis acid.

   Step-by-Step Solution

   1. Statement I: $CO_2$ dissolves in water to give carbonic acid (acidic oxide); $CO$ does not react with water/acids/bases under ordinary conditions (neutral oxide). True.
   2. Statement II: Silica ($SiO_2$) has three crystalline polymorphs: quartz, tridymite, and cristobalite. True.
   3. Statement III: "Dry ice" is the common name for solid carbon dioxide, used as a refrigerant — it is not liquid CO at all. False. …

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3. AP EAPCET 2026Set eng-2026-05-14-FN1 markMCQ
   Q.The number of amphoteric oxides in the following is $CO_2, GeO_2, SnO_2, PbO_2, CO, GeO, SnO, PbO$ The correct answer is (A) 5 (B) 3 (C) 2 (D) 4

   ›Reveal solutionSolution

   $\mathrm{SnO_2},\ \mathrm{PbO_2},\ \mathrm{SnO},\ \mathrm{PbO}$ are amphoteric, giving a count of $4$.

   Concept and Intuition

   Down group 14 oxides shift from acidic to more basic, and for a given element the higher oxidation-state oxide is more acidic than the lower one. Carbon and germanium oxides sit at the acidic/neutral end, while tin and lead oxides (both $+2$ and $+4$) dissolve in both acids and alkalis, i.e. they are amphoteric.

   Step-by-Step Solution

   1. $\mathrm{CO_2}$ — acidic; $\mathrm{CO}$ — neutral: not amphoteric.
   2. $\mathrm{GeO_2}$ — weakly acidic; $\mathrm{GeO}$ — acidic: not counted amphoteric.
   3. $\mathrm{SnO_2}$ — amphoteric.
   4. $\mathrm{PbO_2}$ — amphoteric.
   5. $\mathrm{SnO}$ — amphoteric.
   6. $\mathrm{PbO}$ — amphoteric. …

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4. AP EAPCET 2026Set eng-2026-05-13-AN1 markMCQ
   Q.Which pair of oxides is acidic in nature? (A) $GeO, GeO_2$ (B) $CO, CO_2$ (C) $SnO, SnO_2$ (D) $PbO, PbO_2$

   ›Reveal solutionSolution

   This tests the Group 14 trend in oxide acid–base character, which tracks the increase in metallic character down the group.

   Concept and Intuition

   In Group 14 (C, Si, Ge, Sn, Pb), metallic character increases down the group, and oxide character shifts correspondingly from acidic (top, nonmetals) to amphoteric/basic (bottom, post-transition metals). Germanium sits at the metalloid boundary and still retains predominantly acidic oxide behaviour, unlike tin and lead, whose oxides are well-documented as amphoteric in both oxidation states.

   Step-by-Step Solution

   1. (B) CO, CO2: $CO_2$ is a classic acidic oxide (forms carbonic acid), but $CO$ itself is a neutral (indifferent) oxide — it doesn't react with acids or bases to form a salt. So this pair is not uniformly acidic.
   2. (C) SnO, SnO2: Both oxidation states of tin give amphoteric oxides (react with both acids and bases) — tin is a true metal in this group, so its oxides lean amphoteric rather than acidic.
   3. (D) PbO, PbO2: Similarly, both lead oxides are amphoteric, with $PbO$ showing an even stronger basic tendency (lead is the most metallic element of the group) — not acidic. …

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5. AP EAPCET 2026Set eng-2026-05-15-FN1 markMCQ
   Q.An element X reacts with air to form monoxide and nitride. This oxide is amphoteric. It can be converted to its chloride by heating with carbon and chlorine. Which of the following is correct for X? (A) The oxide of X has rock-salt structure (B) X belongs to group I of the periodic table (C) X shows diagonal relationship with aluminium (D) Carbonate of X is thermally very stable

   ›Reveal solutionSolution

   The clues (monoxide + nitride, amphoteric oxide, carbothermic chlorination) identify X as beryllium, whose defining chemical feature is its diagonal relationship with aluminium.

   Concept and Intuition

   Diagonal relationships in the periodic table occur between a period-2 element and the period-3 element diagonally below-right of it, because their ionic sizes/charge densities happen to be similar even though they're in different groups. Be (group 2) resembles Al (group 13) far more than it resembles its own group-mates (Mg, Ca...) — both form covalent, amphoteric compounds, and both have oxides/chlorides made by similar industrial routes.

   Step-by-Step Solution

   1. "Forms monoxide and nitride": Be reacts with air/$O_2$ to form $BeO$ (a monoxide, unlike Al which forms $Al_2O_3$) and with $N_2$ to form $Be_3N_2$.
   2. "Oxide is amphoteric": $BeO$ is indeed amphoteric (reacts with both acids and bases) — a hallmark Be-Al similarity ($Al_2O_3$ is also amphoteric), unlike the other group-2 oxides (MgO etc., which are basic).
   3. "Converted to chloride by heating with carbon and chlorine": $BeO + C + Cl_2 \xrightarrow{\Delta} BeCl_2 + CO$ — this carbothermic chlorination route is exactly how covalent $Al_2O_3$ is converted to $AlCl_3$ industrially, again reflecting the Be-Al diagonal relationship. …

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6. AP EAPCET 2026Set eng-2026-05-15-FN1 markMCQ
   Q.In group 13 elements, element Y has the lowest boiling point and element Z has lowest melting point. The nature of oxides of Y and Z is respectively (A) Acidic, amphoteric (B) Amphoteric, Basic (C) Basic, amphoteric (D) Amphoteric, amphoteric

   ›Reveal solutionSolution

   Y = Tl (lowest boiling point in group 13) gives a basic oxide (Tl(I), inert-pair effect); Z = Ga (anomalously low melting point) gives an amphoteric oxide — matching "Basic, amphoteric".

   Concept and Intuition

   Group 13 melting/boiling points don't follow a simple monotonic trend because of differences in metallic bonding/crystal packing (Ga in particular has weak metallic bonding with a covalent-like Ga-Ga dimer character in the solid, giving it an unusually low melting point despite being mid-group). Meanwhile the oxidation state matters for oxide acidity: heavier group-13 elements increasingly favour the +1 state (inert pair effect), and +1 oxides of these metals behave more like alkali/alkaline oxides (basic), while +3 oxides (Al, Ga) are typically amphoteric.

   Step-by-Step Solution

   1. Group 13 boiling points (approx.): B $3927^\circ C$, Al $2519^\circ C$, Ga $2204^\circ C$, In $2072^\circ C$, Tl $1473^\circ C$ — lowest is Tl. So Y = Tl.
   2. Group 13 melting points (approx.): B $2076^\circ C$, Al $660^\circ C$, Ga $\approx30^\circ C$ (anomalously low — a well-known fact), In $157^\circ C$, Tl $304^\circ C$ — lowest is Ga. So Z = Ga.
   3. Thallium's most stable oxidation state is $+1$ (inert pair effect dominates for Tl), giving $Tl_2O$ — this behaves as a basic oxide, similar to alkali metal oxides. …

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7. AP EAPCET 2026Set ap-2026-05-19-FN1 markMCQ
   Q.Which of the following is the correct increasing order of atomic number of elements A, B and C of third period, if their oxides are amphoteric, basic and acidic in nature respectively? (A) B, A, C (B) A, B, C (C) C, A, B (D) B, C, A

   ›Reveal solutionSolution

   Oxide character across a period shifts smoothly from basic → amphoteric → acidic as atomic number (and hence non-metallic character) increases; matching that trend to the labelled elements gives the atomic-number order.

   Concept and Intuition

   Moving left to right across period 3 (Na → Cl), metallic character falls and non-metallic character rises. This directly controls oxide character: the leftmost elements (Na, Mg) form basic oxides, the amphoteric borderline is Al (Al₂O₃), and everything to its right (Si, P, S, Cl) forms acidic oxides. So "basic < amphoteric < acidic" in oxide character maps one-to-one onto "lower Z < middle Z (Al) < higher Z."

   Step-by-Step Solution

   1. Identify oxide character to atomic number regions in period 3: basic → Na(11)/Mg(12); amphoteric → Al(13); acidic → Si(14)/P(15)/S(16)/Cl(17). …

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8. AP EAPCET 2026Set ap-2026-05-19-AN1 markMCQ
   Q.Given below are three sets of elements I. $Cs, B, Al$ II. $Ba, S, Be$ III. $In, Pb, Ge$ Identify the sets in which the first, second and third elements can form basic, acidic and amphoteric oxides respectively (A) I, III only (B) II, III only (C) I, II only (D) I, II, III

   ›Reveal solutionSolution

   The key is to classify each element’s oxide as basic (metal, low electronegativity), acidic (nonmetal, high electronegativity), or amphoteric (metalloid or borderline metal). Only set II (Ba, S, Be) fits the pattern: BaO basic, SO₃ acidic, BeO amphoteric. The correct option is (B).

   Concept & Intuition

   Oxides of elements follow periodic trends:

   • Basic oxides form from metals (especially Group 1 and 2) — they react with acids.
   • Acidic oxides form from nonmetals — they react with bases.
   • Amphoteric oxides form from elements near the metal–nonmetal boundary (e.g., Be, Al, Zn, Sn, Pb) — they react with both acids and bases.

   The problem asks: in which set does the first element form a basic oxide, the second an acidic oxide, and the third an amphoteric oxide? We check each set.

   ---

   Step-by-step reasoning

   1. Set I: Cs, B, Al

      • Cs (Cesium): Group 1 metal → oxide Cs₂O is basic. ✓
      • B (Boron): Nonmetal → oxide B₂O₃ is acidic. ✓
      • Al (Aluminum): Metal, but its oxide Al₂O₃ is amphoteric. ✓ So Set I appears to satisfy the pattern. But wait — Al is a metal, and its amphoteric nature is well-known. However, the question expects the third element to be amphoteric, and Al qualifies. So Set I is valid so far.

   2. Set II: Ba, S, Be

      • Ba (Barium): Group 2 metal → BaO is basic. ✓
      • S (Sulfur): Nonmetal → SO₂ or SO₃ are acidic. ✓
      • Be (Beryllium): Metal, but BeO is famously amphoteric (it dissolves in both acids and strong bases). ✓ Set II also satisfies the pattern.

   3. Set III: In, Pb, Ge

      • In (Indium): Metal (Group 13) → In₂O₃ is basic (though weakly amphoteric at high temperatures, but predominantly basic). ✓
      • Pb (Lead): Metal — PbO is amphoteric (not acidic). ✗ The second element must form an acidic oxide, but PbO is amphoteric. PbO₂ is also amphoteric. So this fails.
      • Ge (Germanium): Metalloid — GeO₂ is amphoteric (though slightly more acidic). But the pattern is already broken. …

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9. AP EAPCET 2026Set eng-2026-05-18-AN1 markMCQ
   Q.The nature of chromium oxide formed by the thermal decomposition of ammonium dichromate is (A) acidic (B) basic (C) neutral (D) amphoteric

   ›Reveal solutionSolution

   The chromium oxide from thermally decomposing ammonium dichromate is Cr$_2$O$_3$, a well-known amphoteric oxide.

   Concept and Intuition

   Metal oxide acid-base character often tracks the metal's oxidation state: oxides of metals in low/moderate oxidation states (like Cr$^{3+}$) are frequently amphoteric, reacting with both acids (as a base) and bases (as an acid), while oxides in very high oxidation states tend to be acidic (e.g. $CrO_3$, Cr in +6).

   Step-by-Step Solution

   1. Thermal decomposition: $(NH_4)_2Cr_2O_7 \xrightarrow{\Delta} N_2\uparrow + Cr_2O_3 + 4H_2O$ (the classic "volcano" reaction — green $Cr_2O_3$ ash is a hallmark observation).
   2. $Cr_2O_3$ contains $Cr^{3+}$. …

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10. AP EAPCET 2026Set ap-2026-05-20-FN1 markMCQ
    Q.Which of the following is not correctly matched with respect to the nature of oxides? (A) $SnO, SnO_2$ : Amphoteric nature (B) $CO, CO_2$ : Acidic nature (C) $PbO, PbO_2$ : Amphoteric nature (D) $GeO, GeO_2$ : Acidic nature

    ›Reveal solutionSolution

    CO is a classic example of a neutral oxide (like NO and N2O) — it shows neither acidic nor basic behaviour — so classifying 'CO, CO2' together as 'acidic' is the mismatch.

    Concept and Intuition

    Oxides are classified by their acid–base behaviour: acidic (react with base, e.g. $CO_2$, $SO_2$), basic (react with acid, e.g. $Na_2O$), amphoteric (react with both, e.g. $SnO_2$, $PbO$), and neutral (react with neither — the classic examples taught are CO, NO, and $N_2O$). While $CO_2$ genuinely is an acidic oxide (forms carbonic acid, reacts with bases to form carbonates), CO does not behave as an acidic oxide at all — it is chemically neutral towards both acids and bases, which is why it is grouped separately as a 'neutral oxide' in standard classification.

    Step-by-Step Solution

    1. Check (A): $SnO, SnO_2$ — both amphoteric, a standard fact for tin oxides — correctly matched.
    2. Check (B): $CO$ is a neutral oxide (not acidic!); only $CO_2$ is acidic. Labelling the pair 'acidic' misclassifies CO — incorrectly matched.
    3. Check (C): $PbO, PbO_2$ — both amphoteric, standard fact — correctly matched. …

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11. AP EAPCET 2026Set ap-2026-05-20-AN1 markMCQ
    Q.The nature of oxides of aluminium, boron and gallium are respectively (A) Acidic, amphoteric, basic (B) Amphoteric, acidic, amphoteric (C) Amphoteric, acidic, acidic (D) Basic, acidic, amphoteric

    ›Reveal solutionSolution

    Going down Group 13, the acidic character of the oxide decreases: boron's oxide is acidic, while aluminium's and gallium's oxides are amphoteric.

    Concept and Intuition

    Acid–base character of a p-block element's oxide tracks its metallic character. Boron, at the top of Group 13, behaves more like a non-metal/metalloid, so $B_2O_3$ is acidic. Aluminium and gallium are metallic enough that their oxides show both acidic and basic behaviour (amphoteric), while further down (In, Tl) basic character increases and $Tl_2O_3$ becomes essentially basic.

    Step-by-Step Solution

    1. $B_2O_3$ (boron oxide): boron is the least metallic element of the group; its oxide reacts with bases (forming borates) but not with acids — it is acidic.
    2. $Al_2O_3$ (alumina): reacts with both strong acids (giving $Al^{3+}$ salts) and strong bases (giving aluminates, $[Al(OH)_4]^-$) — it is amphoteric. …

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12. AP EAPCET 2025Set eng-2025-05-22-AN1 markMCQ
    Q.Consider the following Statement-I : $\mathrm{Al_2O_3}$ is amphoteric in nature. Statement-II : $\mathrm{Tl_2O_3}$ is more basic than $\mathrm{Ga_2O_3}$. The correct answer is (A) Both statement-I and statement-II are correct (B) Both statement-I and statement-II are not correct (C) Statement-I is correct, but statement-II is not correct (D) Statement-I is not correct, but statement-II is correct

    ›Reveal solutionSolution

    This tests two group-13 oxide facts — $Al_2O_3$'s amphoteric nature and the down-the-group increase in basicity of $M_2O_3$ oxides — both of which are correct.

    Concept and Intuition

    Across group 13, metallic character increases down the group, and with it the basic character of the trivalent oxides increases: $B_2O_3$ is purely acidic, $Al_2O_3$ and $Ga_2O_3$ are amphoteric, and $In_2O_3$/$Tl_2O_3$ become progressively more basic, reflecting the greater ionic/metallic character of the heavier elements' oxides.

    Step-by-Step Solution

    1. Statement I: $Al_2O_3$ reacts with acids (e.g. HCl) to form aluminium salts, and with bases (e.g. NaOH) to form aluminates — this dual behaviour defines it as amphoteric. Statement I is correct.
    2. Statement II: the basic character of group-13 sesquioxides follows the trend $B_2O_3 < Al_2O_3 \approx Ga_2O_3 < In_2O_3 < Tl_2O_3$, i.e. basicity increases going down the group as the metal becomes more electropositive.
    3. Since Tl lies below Ga in the group, $Tl_2O_3$ is more basic than $Ga_2O_3$ — Statement II is correct. …

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