Substances which have identical chemical properties but differ in atomic weights are called

The mass numbers of two elements $X$ and $Z$ are $52$ and $75$ respectively. $X$ contains $16.6 \%$ more neutrons compared to protons. $Z$ contains $27.3 \%$ more neutrons compared to protons. $X$ and $Z$ are respectively

If the number of neutrons in $_{8}O^{16}$ is doubled and the number of electrons is halved,what is the percentage change in its mass?

Which of the following species are isoelectronic species? $(i)$ $O^{2-}$, $(ii)$ $F^{-}$, $(iii)$ $Na^{+}$, $(iv)$ $Mg^{2+}$

How many neutrons are present in the nucleus of $_{88}Ra^{226}$?

The metal ion with total number of electrons same as $S^{2-}$ is