If a and b are two distinct natural numbers, which one of the following is true ?

Answer: Option C

$$\begin{array}{rl}& \sqrt{a+b}\text{and }\sqrt{a}+\sqrt{b}\\ & \text{Squaring both sides}\\ & (\sqrt{a+b}{)}^2\text{and (}\sqrt{a}+\sqrt{b}{)}^2\\ & \Rightarrow a+b\text{and}a+b+2\sqrt{a}\sqrt{b}\\ & So\sqrt{a+b}<\sqrt{a}+\sqrt{b}\end{array}$$