Which of the following is not a polyamide?

The maximum value of $f(x) = x^4 e^{-x^2}$ is

There is a small hole in a hollow sphere. Water enters it when it is taken to a depth of $40 \, cm$ under water. The surface tension of water is $0.07 \, N/m$. The diameter of the hole is ...... $mm$.

The radius of the larger circle lying in the first quadrant and touching the line $4x + 3y - 12 = 0$ and the coordinate axes is:

$A$ 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:

Which of the following complex ions exhibits optical isomerism? ($en = 1,2$-diaminoethane)