Which of the following is an organometallic compound?

The number of ways of choosing $10$ objects out of $31$ objects,of which $10$ are identical and the remaining $21$ are distinct,is

Which of the following figures represents the variation of particle momentum $p$ and the associated de-Broglie wavelength $\lambda$?

Which of the following is a polyamide?

Four particles $A, B, C$ and $D$ of equal mass $m$ are placed at the four corners of a square. They move with equal uniform speed $v$ towards the intersection of the diagonals. After the collision,particle $A$ comes to rest,particle $B$ traces its path back with the same speed $v$,and particles $C$ and $D$ move with equal speeds $v'$. What is the velocity of particle $C$ after the collision?

$\int \frac{1+x+\sqrt{x+x^2}}{\sqrt{x}+\sqrt{1+x}} d x$ is equal to