Which one among 3 6 ,\, 2 5 and 6 12 is the largest?

Answer: Option B

$$\begin{array}{rl}& \text{root}3\text{of}6,\text{root}2\text{of}5\text{ and }\text{root}6\text{of}12\\ & \text{Take LCM of }\left(3,2\text{ and }6\right)=6\\ & 6^{\frac{1\times 6}{3}},5^{\frac{1\times 6}{2}},12^{\frac{1\times 6}{6}}\\ & 36,125\text{ and }12\\ & \text{Clearly, }\text{root}2\text{of}5\text{ is the largest}\text{.}\end{array}$$