Which pair of symbols represent nuclei that have the same number of neutrons?

The symbols represent nuclei that have the same number of neutrons is ${ }_{26}^{56}\mathrm{Fe}$ and ${ }_{28}^{58}\mathrm{Ni}$.

Number of neutron = ( Atomic mass - Atomic number )

(A)${ }_{26}^{56}\mathrm{Fe}$ and ${ }_{28}^{58}\mathrm{Ni}$ have same number of neutrons, $56-26=30$ and $58-28=30$respectively.

(B) ${ }_{26}^{58}\mathrm{Fe}$ and ${ }_{26}^{56}{\mathrm{Fe}}^{2+}$ have different number of neutrons, $58-26=32$ and $56-26=30$ respectively.

(C) ${ }_{27}^{57}\mathrm{Co}$ and ${ }_{27}^{57}\mathrm{Ni}$ have different number of neutrons, $57-27=30$ and $57-28=29$ respectively.

(D) ${ }_{28}^{57}\mathrm{Ni}$ and ${ }_{28}^{58}\mathrm{Ni}$ have different number of neutrons, $57-28=29$ and $58-28=30$ respectively.

Thus, ${ }_{26}^{56}\mathrm{Fe}$ and ${ }_{28}^{58}\mathrm{Ni}$ have the same number of neutrons.

Hence, the option A is correct.