Humoral immunity is due to

$A$ plank with a small block on top of it is undergoing vertical $SHM$. Its period is $2 \, s$. The minimum amplitude at which the block will separate from the plank is:

$A$ gaseous mixture contains $50\%$ helium and $50\%$ methane by volume. What is the percentage of methane by weight in the mixture?

If the direction cosines of two lines are given by $l+m+n=0$ and $l^2-5m^2+n^2=0$,then the angle between them is

If $m \begin{bmatrix} -3 & 4 \end{bmatrix} + n \begin{bmatrix} 4 & -3 \end{bmatrix} = \begin{bmatrix} 10 & -11 \end{bmatrix}$,then $3m + 7n$ is equal to

If the angles of a triangle are in the ratio $4:1:1$,then the ratio of the longest side to the perimeter is