Which compound is soluble in $NH_4OH$?

The function $f: R \rightarrow R$ defined by $f(x)=\frac{x}{\sqrt{1+x^2}}$ is ........

$A$ circle passes through the point $(3, 4)$ and cuts the circle $x^2 + y^2 = a^2$ orthogonally. The locus of its centre is a straight line. If the distance of this straight line from the origin is $25$,then $a^2$ is equal to

If the slope of one line is twice the slope of the other in the pair of straight lines $ax^2 + 2hxy + by^2 = 0$,then $8h^2$ is equal to (in $ab$)

An ideal coil of $10\,H$ is connected in series with a resistance of $5\,\Omega$ and a battery of $5\,V$. After $2\,s$ the connection is made,the current flowing in ampere in the circuit is

Assuming the diodes to be of silicon with forward resistance zero,the current $I$ in the following circuit is.......$mA$