The number of octahedral and tetrahedral holes respectively present in a hexagonal close packed $(hcp)$ crystal of '$X$' atoms are

If the $x$-coordinate of a point $P$ on the line joining the points $Q(2, 2, 1)$ and $R(5, 1, -2)$ is $4$,then the $z$-coordinate of $P$ is

The line joining the points $A(2,0)$ and $B(3,1)$ is rotated through an angle of $45^{\circ}$ about $A$ in the anti-clockwise direction. Find the coordinates of $B$ in the new position.

The molarity of a $0.2 \ N \ Na_2CO_3$ solution will be .......... $M$.

$A$ body of mass $M \ kg$ is at the top point of a smooth hemisphere of radius $5 \ m$. It is released to slide down the surface of the hemisphere. It leaves the surface when its velocity is $5 \ m/s$. At this instant,the angle made by the radius vector of the body with the vertical is: (Acceleration due to gravity $g = 10 \ m/s^2$) (in $^{\circ}$)

$A$ three-digit number $n$ is such that the last two digits are equal and differ from the first digit. The number of such $n$'s is: