SOLUTION :
$\left(\frac{1}{9}\right)^{a}=\left(\frac{1}{9}\right)^{-4} \times\left(\frac{1}{27}\right)^{-6}$
$\Rightarrow\left(\frac{1}{3}\right)^{2 a}=\left(\frac{1}{3}\right)^{-8} \times\left(\frac{1}{3}\right)^{-18}$
$\Rightarrow\left(\frac{1}{3}\right)^{2 a}=\left(\frac{1}{3}\right)^{-26}$
$\Rightarrow 2 a=-26$
$\therefore \quad a=-\frac{26}{2}=-13 ;$ Ans.
Therefore, The correct option is $(\mathrm{B})$