Which property is different for neutral atoms of the two isotopes of the same element?

Which of the following is not isoelectronic with $O^{2-}$?

The ratio between the number of neutrons in $C$ (atomic mass $12$) and $Si$ (atomic mass $28$) is

Chemical behaviour of an atom is determined by

The atomic number of bromine is $35$ and its atomic weight is $79$. Two isotopes of bromine are present in equal amounts. Which of the following statements represents the correct number of neutrons?

In the neutral state,the element $M$ consists of the isotopes $_{14}M^{28}$,$_{14}M^{29}$,and $_{14}M^{30}$ in the ratio $60 : 30 : 20$ respectively. Correct statements about $M$ in the natural state include that: