Let $u$ and $v$ be two vectors. Then,$|u-v|=||u|-|v||$ if and only if

$A$ certain number of spherical drops of a liquid of radius $r$ coalesce to form a single drop of radius $R$ and volume $V$. If $T$ is the surface tension of the liquid,then:

Starting from rest, the time taken by a body sliding down on a rough inclined plane at $45^{\circ}$ with the horizontal is twice the time taken to travel on a smooth plane of the same inclination and same distance. Then the coefficient of kinetic friction is:

The magnetic moment of a complex ion is $2.83 \ BM$. The complex ion is

The angles of a triangle are in the ratio $3: 5: 10$. Then the ratio of the smallest side to the greatest side is:

The number of unpaired electrons in $Zn^{2+}$ is