Q.Calculate the number of protons, neutrons and electrons in $^{80}_{35}Br$.

Showing the 12 most recent of 20 on this concept.

1. CBSE 2026Set ANNUAL1 markMCQ
   Q.If the number of protons and neutrons of an element is 13 and 14 respectively, then what are the atomic number (Z) and mass number (A)?

   (a) 13, 13

   (b) 13, 27

   (c) 14, 13

   (d) 27, 14

   ›Reveal solutionSolution

   Atomic number (Z) equals the number of protons; mass number (A) equals the sum of protons and neutrons.

   Given: number of protons = 13, number of neutrons = 14.

   Atomic number, Z = number of protons = 13.

   Mass number, A = number of protons + number of neutrons = 13 + 14 = 27.

   So Z = 13 and A = 27 (this element is aluminium, Al).

   ✓Final answer

   (b) 13, 27 -- Z = 13 (protons), A = 27 (protons + neutrons).

2. CBSE 2026Set ANNUAL1 mark
   Q.In ⁸⁰₃₅Br, the number of neutrons is ______.

   ›Reveal solutionSolution

   The bromine nuclide with mass number 80 and atomic number 35 has 45 neutrons.

   A nuclide is written as (mass number)/(atomic number) Symbol, i.e., mass number A on top and atomic number Z below, attached to the element symbol. Here A = 80 (mass number = total number of protons + neutrons) and Z = 35 (atomic number = number of protons, which equals bromine's atomic number). Number of neutrons N = A - Z = 80 - 35 = 45.

   ✓Final answer

   The number of neutrons is 45.

3. CBSE 2026Set ANNUAL1 markMCQ
   Q.If atomic mass of an element is 23 and its atomic number is 11, then the number of neutrons in an atom of the element would be

   (a) 23

   (b) 12

   (c) 11

   (d) 34

   ›Reveal solutionSolution

   Neutrons = mass number − atomic number = 23 − 11 = 12.

   Atomic number (Z) = number of protons = 11. Mass number (A) = protons + neutrons = 23.

   Neutrons = A − Z = 23 − 11 = 12. (This element is sodium.)

   ✓Final answer

   (B) 12.

4. CBSE 2026Set ANNUAL1 markMCQ
   Q.Atoms having same atomic number but different mass numbers are called

   (a) Polymers

   (b) Isomers

   (c) Isotopes

   (d) Isobars

   ›Reveal solutionSolution

   Same atomic number, different mass number = isotopes.

   Isotopes are atoms of the same element (same number of protons, same Z) that differ in the number of neutrons, hence different mass numbers. Example: 1H, 2H, 3H. (Isobars have the same mass number but different atomic numbers.)

   ✓Final answer

   (C) Isotopes.

5. CBSE 2025Set ANNUAL1 markMCQ
   Q.Calculate the number of electrons, protons and neutrons in 35Br80.

   (a) 35, 45, 35

   (b) 35, 35, 45

   (c) 35, 36, 45

   (d) 36, 35, 45

   ›Reveal solutionSolution

   For a neutral atom, protons = electrons = atomic number (Z); neutrons = mass number (A) - Z. For 35Br80: 35 protons, 35 electrons, 45 neutrons.

   The notation ZX^A (or here, 35Br80) gives the atomic number Z = 35 as a subscript and the mass number A = 80 as a superscript, for the element bromine (Br).

   Step 1 — Protons: The atomic number Z directly equals the number of protons in the nucleus.

   Protons = Z = 35

   Step 2 — Electrons: In a neutral (uncharged) atom, the number of electrons equals the number of protons.

   Electrons = 35

   Step 3 — Neutrons: The mass number A is the total count of protons + neutrons.

   Neutrons = A - Z = 80 - 35 = 45

   So the atom has 35 electrons, 35 protons, and 45 neutrons — matching the order asked in the question (electrons, protons, neutrons).

   ✓Final answer

   (b) 35, 35, 45.

6. CBSE 2025Set ANNUAL1 markMCQ
   Q.An ion B^2- has 18 electrons and 16 neutrons. Its mass number will be -

   (a) 34

   (b) 32

   (c) 18

   (d) 16

   ›Reveal solutionSolution

   For B2- with 18 electrons and 16 neutrons, the number of protons is 16 (since the 2- charge means 2 extra electrons over protons), giving mass number = 16 + 16 = 32.

   A B2- ion carries a charge of -2, meaning it has 2 more electrons than protons (since each extra electron adds one unit of negative charge).

   Number of electrons = 18

   Number of protons (Z) = electrons - (charge magnitude, since anion) = 18 - 2 = 16

   Mass number (A) = number of protons + number of neutrons = 16 + 16 = 32

   ✓Final answer

   The correct option is (b) 32.

7. CBSE 2025Set ANNUAL1 mark
   Q.Give one example of isotones.

   ›Reveal solutionSolution

   Isotones = same neutron count, different element; e.g. 14C (8n) and 15N (8n).

   Isotones are atoms of different elements that have the same number of neutrons (but different atomic numbers and different mass numbers). Number of neutrons = mass number − atomic number.

   Example: $^{14}_{6}C$ has $14-6=8$ neutrons, and $^{15}_{7}N$ has $15-7=8$ neutrons — both have 8 neutrons, so they are isotones of each other. (Other valid examples include $^{30}_{14}Si$ and $^{31}_{15}P$, both with 16 neutrons.)

   ✓Final answer

   $^{14}_{6}C$ and $^{15}_{7}N$ (both have 8 neutrons) are isotones.

8. CBSE 2024Set ANNUAL1 markMCQ
   Q.By which of the following is positron represented?

   (a) 0/-1 e

   (b) 0/+1 e

   (c) 1/1 H

   (d) None of these

   ›Reveal solutionSolution

   Positron is represented as ⁰₊₁e — zero mass number (in nucleon terms), +1 charge.

   A positron is a positively charged particle with the same (negligible, ~1/1837 amu) mass as an electron, so its mass number is written as 0, and its charge is +1. It is represented as ⁰₊₁e, in contrast to the electron ⁰₋₁e.

   ✓Final answer

   (B) ⁰₊₁e.

9. CBSE 2024Set ANNUAL1 markMCQ
   Q.Match the correct pair -- the isotope written as mass number 80, atomic number 35 (Bromine-80, ^80_35Br) should be matched with the correct item from Column B:

   (a) 45 Neutron

   (b) Octahedral

   (c) mol L^-1

   (d) ΔS = q(rev)/T

   (e) (triangle symbol, drawn as a downward-pointing triangle -- representing a 3-membered ring shape)

   ›Reveal solutionSolution

   Number of neutrons = mass number (A) - atomic number (Z). For A = 80, Z = 35 (Bromine-80): neutrons = 80 - 35 = 45, matching option (a).

   The notation ^A_Z X gives mass number A (protons + neutrons) and atomic number Z (protons, = number of electrons in a neutral atom). Here A = 80, Z = 35, so:

   Number of neutrons = A - Z = 80 - 35 = 45.

   ✓Final answer

   ^80_35Br -- (a) 45 Neutron.

10. CBSE 2022Set TERM11 markMCQ
    Q.Number of protons, neutrons and electrons in the element 89X^231 is

    (a) 89, 89, 242

    (b) 89, 142, 89

    (c) 89, 71, 89

    (d) 89, 231, 89

    ›Reveal solutionSolution

    For a neutral atom written as (mass number)X(atomic number): protons = atomic number, neutrons = mass number - atomic number, electrons = protons.

    Here the atomic number (subscript, number of protons) is 89, and the mass number (superscript, protons + neutrons) is 231.

    • Protons = atomic number = 89
    • Neutrons = mass number - atomic number = 231 - 89 = 142
    • Electrons = protons (neutral atom) = 89

    So the set is 89 protons, 142 neutrons, 89 electrons.

    ✓Final answer

    (b) 89, 142, 89.

11. CBSE 2022Set ANNUAL1 markMCQ
    Q.If atomic number of an element is 25 and its atomic mass is 55, then its nucleus contains:

    (a) 25 Protons and 3 neutrons

    (b) 55 Proton

    (c) 25 Protons and 30 neutrons

    (d) 55 neutrons

    ›Reveal solutionSolution

    With atomic number 25 and mass number 55, the nucleus has 25 protons and 30 neutrons.

    The atomic number (Z) of an element is, by definition, the number of protons in the nucleus - so Z = 25 means the nucleus contains 25 protons. The mass number (A) is the total count of nucleons (protons + neutrons): A = Z + n, so 55 = 25 + n, giving n = 55 - 25 = 30. So the nucleus contains 25 protons and 30 neutrons. Options (b) and (d) wrongly assume all 55 mass units are one kind of particle, and the rival choice of 25 protons with only 3 neutrons badly undercounts the neutrons.

    ✓Final answer

    The correct option is (c) 25 Protons and 30 neutrons.

12. CBSE 2022Set ANNUAL1 mark
    Q.Write the Atomic number of Copper.

    ›Reveal solutionSolution

    Copper's atomic number is 29.

    Atomic number (Z) equals the number of protons in the nucleus of an atom, which also equals the number of electrons in a neutral atom. Copper (Cu), a Group 11 transition metal, has 29 protons and 29 electrons, giving it the electronic configuration [Ar] 3d10 4s1 (an exception to the normal filling order, since a fully filled 3d10 subshell is extra stable).

    ✓Final answer

    The atomic number of copper (Cu) is 29.