Q.What are the common physical and chemical features of alkali metals ?

Physical features

• Soft metals that can be cut with a knife; softness increases down the group.
• Silvery-white lustre when freshly cut, tarnishes rapidly in air.
• Low density (increases roughly down the group, with an anomaly at K), low melting and boiling points that decrease down the group.
• Good conductors of heat and electricity.
• Large atomic and ionic radii for their period; radii increase down the group.

Chemical features

• Outer electronic configuration ns$^1$ (one electron beyond a noble-gas core), so they are strongly electropositive and univalent (+1).
• Very low ionisation enthalpy, decreasing down the group, making them powerful reducing agents.
• React vigorously with water: $2M + 2H_2O \rightarrow 2MOH + H_2\uparrow$
• React with oxygen to give oxides (Li), peroxides (Na) or superoxides (K, Rb, Cs).
• React directly with halogens to form ionic halides, and with hydrogen to form ionic (saline) hydrides.
• Form strongly basic hydroxides and salts that are, with few exceptions, water-soluble.
• Impart characteristic colours to a flame (except Li being faint) due to easily excited outer electrons.
• Dissolve in liquid ammonia to give blue, electrically-conducting solutions containing solvated (ammoniated) electrons.

List the shared physical traits (soft, low density, low m.p./b.p., good conductors) and shared chemical traits (ns$^1$ configuration, low ionisation enthalpy, +1 oxidation state, strong reducing agents, reaction with water/oxygen/halogens/hydrogen) that flow directly from having one loosely-held valence electron.

• Listing only physical or only chemical properties instead of covering both, as the question asks.
• Forgetting the group-wise variation (e.g. that Li forms only the normal oxide while Na gives a peroxide and K/Rb/Cs give superoxides) and stating a single blanket reaction for all.
• Omitting the ammonia-solution behaviour, a distinctive chemical feature of the group.