Which of the following is not a Lewis acid?

Two bodies of mass $4 ~kg$ and $5 ~kg$ are moving along east and north directions with velocities $5 ~m/s$ and $3 ~m/s$ respectively. The magnitude of the velocity of the centre of mass of the system is

$\int \frac{dx}{a^2 \sin^2 x + b^2 \cos^2 x}$ is equal to

If $\frac{3+2i \sin \theta}{1-2i \sin \theta}$ is a real number and $0 < \theta < 2\pi$,then $\theta$ is equal to

The species with spin only magnetic moment of $\sqrt{24} \ BM$ is

The ratio of the magnetic field at the centre of a current-carrying circular coil to its magnetic moment is $x$. If the current and the radius are both doubled,the new ratio will become: