Ratio of SI unit of torque to its CGS unit is : 

As you know, torque (T) is the cross product of force (F) and length (L).

$T=F\times L$

As we all know that the S.I unit of force is Newton (N) and the S.I unit of length is meter.
So, the S.I unit of torque is N-m.
And the CGS unit of torque is Dyne-Centimeter (dyne-Cm).
Now as we all know that
$1 Newton = 100000 Dyne.$
And $1 m = 100 cm.$
So, $1 N.m = 100000\times 100 dyn.cm$

$\Rightarrow 1N.m={10}^{7}dyn.cm$
$\Rightarrow \frac{1N.m}{1dyn.cm}={10}^7$
So, the ratio of the S.I unit of torque to the C.G.S unit of torque is${10}^7$.
Hence, the correct answer is option A.