The condition for the lines $lx + my + n = 0$ and $l_1x + m_1y + n_1 = 0$ to be conjugate with respect to the circle $x^2 + y^2 = r^2$ is

$A$ man fires a bullet standing between two cliffs. The first echo is heard after $3 \ s$ and the second echo is heard after $5 \ s$. If the velocity of sound is $330 \ m/s$,then the distance between the cliffs is .... $m$.

Assertion : Between any two given energy levels,the number of absorption transitions is always less than the number of emission transitions.
Reason : Absorption transitions start from the lowest energy level only and may end at any higher energy level. But emission transitions may start from any higher energy level and end at any energy level below it.

$\frac{3\sqrt{2}}{\sqrt{6} + \sqrt{3}} - \frac{4\sqrt{3}}{\sqrt{6} + \sqrt{2}} + \frac{\sqrt{6}}{\sqrt{3} + \sqrt{2}} = $

$P_4O_{10}$ has short and long $P-O$ bonds. The number of short $P=O$ bonds in this compound is

In $........$ and $........$ organisms or the parent cell divides into two to give rise to new individuals.