In an ellipse,the distance between its foci is $6$ and its minor axis is $8$. Then its eccentricity is

The average degree of freedom per molecule of a gas is $6$. The gas performs $25 \ J$ of work while expanding at constant pressure. The heat absorbed by the gas is .... $J$.

Which of the following elements shows polymorphism?

Assertion : Energy is released when heavy nuclei undergo fission or light nuclei undergo fusion.
Reason : For heavy nuclei,binding energy per nucleon increases with increasing $Z$ while for light nuclei it decreases with increasing $Z$.

Match the appropriate pairs from List-$I$ and List-$II$ :

List-$I$	List-$II$
$1$. Nitrogen molecules	$(A)$ Continuous spectrum
$2$. Incandescent solids	$(B)$ Absorption spectrum
$3$. Fraunhoffer lines	$(C)$ Band spectrum
$4$. Electric arc between iron rods	$(D)$ Emission spectrum

$\Delta \lambda$ is the difference between the wavelength of the $K_{\alpha}$ line and the minimum wavelength of the continuous $X$-ray spectrum when the $X$-ray tube is operated at a voltage $V$. If the operating voltage is changed to $V/3$,then the above difference is $\Delta \lambda^{\prime}$. Then: