Which of the following is correct?

• Correct answer
  A

  The number of electrons present in the valence shell of $\mathrm{S}$ in $\mathrm{SF}_6$ is 12
• B

  The rates of ionic reactions are very slow
• C

  According to VSEPR theory, $\mathrm{SnCl}_2$ is a linear molecule
• D

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

Solution

$\mathrm{SF}_6$ does not obey octet rule as in it S-atom has 12 electrons in its valence shell.

Hence, the correct answer is option: 'A'.