The ratio of a number of valence shell electrons to the number of penultimate shell electrons in $Y^{-2}$ are:
(Atomic number of $Y$ is $34$)

The correct option is B $4/9$
The electronic configuration for $Y^{2-}$ is:

$\Rightarrow Y^{2-}=1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^6$

Here, valence shell electrons= $8$

Penultimate shell= $3$ $\therefore$ Penultimate shell electrons= $18$

$\therefore$ Ratio= $8:18=4:9$