The number of atoms in $100 \text{ g}$ of an $fcc$ crystal with density $d = 10 \text{ g/cm}^3$ and cell edge equal to $100 \text{ pm}$ is equal to:

The vector sum of two forces is perpendicular to their vector difference. In that case,the forces

If $L: ax + by + c = 0$ is a variable straight line,where $a, b$ and $c$ are the second,fourth and seventh terms of an $AP$ respectively,then $L$ passes through the fixed point -

Which one of the following is mainly responsible for the depletion of the ozone layer?

In a circuit,the current lags behind the voltage by a phase difference of $\pi / 2$. The circuit contains which of the following?

$A$ capacitor of capacity $0.1 \mu F$ connected in series to a resistor of $10 M \Omega$ is charged to a certain potential and then made to discharge through the resistor. The time in which the potential will take to fall to half its original value is (Given,$\log _{10} 2=0.3010$ ) (in $~s$)