Answer: $\text C$
Let $\mathrm{a = 1.x, \;b = \sqrt 3x, ~c= 2x}$
Now,
$\mathrm{a^2 + b^2 = x^2 + (\sqrt3x)^2 = x^2 + 3x^2 = 4x^2 = \bf{c^2}}$
$ \Rightarrow $This is a Right Triangle.
Now, the angle opposite to the biggest side will be the right angle.
$\therefore \mathrm{\angle C \text{ is the right angle.}}$
Now,
$\mathrm {\sin A = \frac{a}{c} = \frac{x}{2x} = \frac{1}{2} \Rightarrow A = 30^0}$
Now,
$\mathrm{\angle C = 180^0 - 30^0 = 60^0}$
$\therefore \mathrm{A:B:C = 30:60:90 = 1:2:3}$
$\therefore \mathbf C$ is the correct option.