Which of the following is correct ?

Question

(a) The number of electrons present in the valence shell of S in $SF_6$ is 12.

(b) The rates of ionic reactions are very slow

(c) According to VSEPR theory,$SnCl_2$ is a linear molecule

(d) The correct order of ability to form ionic compounds among $Na^{+},Mg^{2+}$ and $Al^{3+}$ is $Al^{3+} > Mg^{2+} > Na^{+}$