Which of the following is a primary lymphoid organ?

$A$ body of mass $1 ~g$ and carrying a charge $10^{-8} ~C$ passes through two points $P$ and $Q$. $P$ and $Q$ are at electric potentials $600 ~V$ and $0 ~V$,respectively. The velocity of the body at $Q$ is $20 ~cm/s$. Its velocity in $m/s$ at $P$ is:

The binding energy of deuteron ${}_1^2H$ is $1.112 \text{ MeV}$ per nucleon and an $\alpha$-particle ${}_2^4He$ has a binding energy of $7.047 \text{ MeV}$ per nucleon. Then in the fusion reaction ${}_1^2H + {}_1^2H \to {}_2^4He + Q$,the energy $Q$ released is ........... $\text{MeV}$.

Let $n = 1! + 4! + 7! + \ldots + 400!$. Then the ten's digit of $n$ is

The maximum tension a rope can withstand is $60 ~kg-wt$. The ratio of maximum acceleration with which two boys of masses $20 ~kg$ and $30 ~kg$ can climb up the rope at the same time is

The coefficient of $x^5$ in the expansion of $(1 + x)^{21} + (1 + x)^{22} + \dots + (1 + x)^{30}$ is