Sulfide ores are common for the metals:

$A$ metallic wire with tension $T$ and at temperature $30^{\circ} C$ vibrates with its fundamental frequency of $1 \ kHz$. The same wire with the same tension but at $10^{\circ} C$ temperature vibrates with a fundamental frequency of $1.001 \ kHz$. The coefficient of linear expansion of the wire is

If three vectors $a, b, c$ satisfy $a + b + c = 0$ and $|a| = 3, |b| = 5, |c| = 7$,then the angle between $a$ and $b$ is ............ $^\circ$.

Exhausted permutit does not contain $.......$ ion.

The electronic configurations of four elements are given as:
$(I) 1s^2, (II) 1s^2 2s^2 2p^2, (III) 1s^2 2s^2 2p^5, (IV) 1s^2 2s^2 2p^6$. Which configuration has the ability to form both ionic and covalent bonds?

$NPN$ transistors are preferred to $PNP$ transistors because they have