The $pK_a$ of a weak acid is $4.8$. What should be the ratio of $\frac{[\text{acid}]}{[\text{salt}]}$,if a buffer of $pH=5.8$ is required?

Assertion $(A)$: Optical fibres are widely used in communication networks. Reason $(R)$: Optical fibres are small in size,light in weight,flexible,and there is no scope for interference in them.

$A$ photon of energy $E$ ejects a photoelectron from a metal surface whose work function is $W_0$. If this electron enters into a uniform magnetic field of induction $B$ in a direction perpendicular to the field and describes a circular path of radius $r,$ then the radius $r$ is given by: (in the usual notation)

Two coherent monochromatic light beams of intensities $I$ and $4I$ are superposed. The maximum and minimum possible intensities in the resulting beam are:

$A$ car is moving at a speed of $40 \, m/s$ on a circular track of radius $400 \, m$. This speed is increasing at the rate of $3 \, m/s^2$. The acceleration of the car is ....... $m/s^2$.

Consider a thin uniform square sheet made of a rigid material. If its side is $a$,mass is $m$,and moment of inertia about one of its diagonals is $I$,then: