Two identical charged spherical drops, each of capacitance $C$, merge to form a single drop. The resultant capacitance is:

Along the $x$-axis,three charges $\frac{q}{2}, -q$ and $\frac{q}{2}$ are placed at $x=0, x=a$ and $x=2a$ respectively. The resultant electric potential at a point $P$ located at a distance $r$ from the charge $-q$ (where $r > a$) is ($\varepsilon_0$ is the permittivity of free space):

Match the following:

List-$I$	List-$II$
$(A)$ Electron deficient hydride	$(I)$ $CH_4$
$(B)$ Electron precise hydride	$(II)$ $B_2H_6$
$(C)$ Electron rich hydride	$(III)$ $CaH_2$
$(D)$ Saline hydride	$(IV)$ $NiH_{0.6}$
	$(V)$ $PH_3$

Which structure in the embryo is considered the precursor to the urinary bladder?

$A$ wind with speed $40\,m/s$ blows parallel to the roof of a house. The area of the roof is $250\,m^2.$ Assuming that the pressure inside the house is atmospheric pressure,the force exerted by the wind on the roof and the direction of the force will be $(\rho_{air} = 1.2\,kg/m^3)$

The acceleration due to gravity on the moon is $\left(\frac{1}{6}\right)$ times the acceleration due to gravity on the earth. If the ratio of the density of the earth $\rho_{e}$ to the density of the moon $\rho_{m}$ is $\frac{5}{3}$,then the radius of the moon $R_{m}$ in terms of the radius of the earth $R_{e}$ is: