The potential energy between two atoms in a molecule is given by $U(x) = \frac{a}{x^{12}} - \frac{b}{x^6}$,where $a$ and $b$ are positive constants and $x$ is the distance between the atoms. The atoms are in stable equilibrium when:

Root cap is absent in

The total number of $\sigma$ and $\pi$-bonds in pyrophosphoric acid are respectively

In $YDSE$,how many maxima can be obtained on the screen if the wavelength of light used is $200 \, nm$ and $d = 700 \, nm$?

Two cylinders $A$ and $B$ fitted with pistons contain equal number of moles of an ideal monoatomic gas at $400 ~K$. The piston of $A$ is free to move while that of $B$ is held fixed. Same amount of heat energy is given to the gas in each cylinder. If the rise in temperature of the gas in $A$ is $42 ~K$,the rise in temperature of the gas in $B$ is (in $~K$)

Match Column-$I$ with Column-$II$ and select the correct option.

Column-$I$	Column-$II$
$A$. Fishes	$(i)$. Three-chambered heart
$B$. Amphibians	$(ii)$. Incomplete double circulation
$C$. Birds	$(iii)$. Four-chambered heart
	$(iv)$. Single circulation
	$(v)$. Two-chambered heart
	$(vi)$. Double circulation