The transition metal ions responsible for colour in ruby and emerald are respectively :

The transition metal ions responsible for colour in ruby and emerald is ${\mathrm{Cr}}^{3+}\text{ and }{\mathrm{Cr}}^{3+}$.

Ruby is $\mathrm{Al}{ }_2{\mathrm{O}}_3$ and the red colour is achieved by substituting ${\mathrm{Al}}^{+3}$ ions in octahedral positions with ${\mathrm{Cr}}^{+3}$. Emerald is $B{e}_{3}A{l}_2{\left({\mathrm{SiO}}_3\right)}_6$, which gets its green colour when ${\mathrm{Cr}}^{+3}$  replaces ${\mathrm{Al}}^{+3}$ in the octahedral site.

Therefore, option A is correct.