Which oxide of manganese is amphoteric?

Which of the following elements shows polymorphism?

Which one of the following conditions correctly describes the manner of determining the sex?

The voltage of an $AC$ source varies with time according to the equation $V = 100 \sin(100\pi t) \cos(100\pi t)$,where $t$ is in seconds and $V$ is in volts. Then:

Two cards are drawn successively with replacement from a well-shuffled pack of $52$ cards. The mean of the number of kings is:

The parabola with directrix $x+2y-1=0$ and focus $(1,0)$ is