Question

An element $X$ has two isotopes, which may be represented as ${}^{238}X$ and ${}^{235}X$.
How does ${}^{238}X$ differ from ${}^{235}X$?

• A. ${}^{238}X$ has $3$ more protons and $3$ more electrons than $235$
• B. ${}^{238}X$ has $3$ more electrons, but same number of protons as $235$
• C. ${}^{238}X$ has $3$ more neutrons, but the electrons or protons are same as $235$
• D. ${}^{238}X$ has $3$ more protons, but same number of electrons as $235$

Answer 1

The correct option is C ${}^{238}X$ has $3$ more neutrons, but the electrons or protons are same as $235$

${}^{238}X{,}^{235}X$ are isotopes hence has same atomic number, i.e. same number of protons and electrons however their mass number is different hence ${}^{238}X$ has $238-235$ i.e., $3$ more neutrons as ${}^{235}X$. Hence answer is option C.