Which of these is least likely to act as a Lewis base?

Which among the following is $NOT$ a feature of $S_N2$ mechanism?

If the angle between the asymptotes of the hyperbola $\frac{x^2}{a^2} - \frac{y^2}{3} = 4$ is $\frac{\pi}{3}$,then its conjugate hyperbola is:

The angle between a pair of tangents drawn from a point $P$ to the circle $x^{2}+y^{2}+4x-6y+9 \sin^{2} \alpha + 13 \cos^{2} \alpha = 0$ is $2 \alpha$. The equation of the locus of the point $P$ is

In the circuit shown in the figure,neglecting source resistance,the voltmeter and ammeter readings will respectively be:

Identify the product $(C)$ in the following series of reactions:
Cyclopentane $\xrightarrow{Br_2 (1 \ eq), h\nu} (A)$ $\xrightarrow{Alc. KOH} (B)$ $\xrightarrow{NBS} (C)$