JEE Main · 2023 · 06 Apr 2023 · Shift 1 · Atomic Structure

When a hydrogen atom loses its only electron, what remains is the bare nucleus, a proton whose radius is of the order of $1.5\times 10^{-3}\mathrm{pm}$, far smaller than an atom, so the assertion is correct. The reason, that the free proton is so reactive that it never exists alone but always in a combined form such as ${\mathrm{H}}_3{\mathrm{O}}^{+}$, is also a correct statement. However, the reason describes the chemical behaviour of the proton and does not account for its extremely small size, so it is not the explanation of the assertion. Both A and R are correct but R is not the correct explanation of A.