Consider the following statements:
$A$. Atoms of each element emit characteristic spectrum.
$B$. According to Bohr's postulate, an electron in a hydrogen atom revolves in a certain stationary orbit.
$C$. The density of nuclear matter depends on the size of the nucleus.
$D$. A free neutron is stable but a free proton decay is possible.
$E$. Radioactivity is an indication of the instability of nuclei.
Choose the correct answer from the options given below.
Answer: (B) $A$, $B$ and $E$ only
$A$: true, every element has its own line spectrum.
$B$: true, Bohr's postulate of stationary orbits.
$C$: false, $R \propto A^{1/3}$, so nuclear density is the same for all nuclei.
$D$: false, a free neutron decays (half-life about $10$ min) while a free proton is stable.
$E$: true. Hence $A$, $B$ and $E$ only.
Solution by Sreeraj P, M.Sc Physics