Watch out, this bob might hit you unawares!

The component in the vertical direction :

$mg \times \cos \theta$

$= \frac{\sqrt3}{2} \times mg$

ok if u get this wrong , no problem. I was also wrong on the first attempt.

Force will be balanced along the string as there is no acceleration along the string .

So $T=\frac{\sqrt{3}}{2}mg$

Do upvote

The key thing to note is that the system is a pendulum, which has a periodic circular motion. This implies that when the ball is released, there is a force tangential to the arc (ie perpendicular to the radius).

By Newton's second law of motion, $F_{\text{net,rad}} = 0$ . Since the two forces are the weight of the bob $mg$ and the tension in the string $T$ , we then know that

$T = mg\cos 30^{\circ} = \boxed{\frac{\sqrt{3}}{2}mg}$

after resolving the vectors.