The period of f(x)=sin 5 x+cos √3 x is :

Period of $\sin 5 x$ is $2 \pi / 5$

Period of $\cos \sqrt{3}x$ is $\frac{2 \pi}{3}$

for the period of f(x) LCM of $2 \pi / 5$ and $\frac{2 \pi}{\sqrt{3}}$, which doesn't exist.

Hence f(x) is non-periodic

Hence (4) is the correct answer.