What is the gas liberated when alkaline formaldehyde solution is treated with $H_2O_2$?

The point of intersection of tangents at the ends of the latus rectum of the parabola $y^2 = 4x$ is equal to

The arrangement of $X^{-}$ ions around $A^{+}$ ion in solid $AX$ is given in the figure. If the radius of $X^{-}$ is $250 \ pm$,the radius of $A^{+}$ is ............. $pm$.

For $k=1, 2, 3$, the box $B_k$ contains $k$ red balls and $(k+1)$ white balls. Let $P(B_1)=\frac{1}{2}$, $P(B_2)=\frac{1}{3}$, and $P(B_3)=\frac{1}{6}$. $A$ box is selected at random and a ball is drawn from it. If a red ball is drawn, then the probability that it has come from box $B_2$ is:

${}^{18}_{8}O$ has a half-life of $4650 \ years$. $200 \ mg$ of a sample of ${}^{18}_{8}O$ is reduced to $25 \ mg$ in .......... $years$.

Which one of the following population interactions is widely used in medical science for the production of antibiotics?