In a binary compound,atoms of element $A$ form a $hcp$ structure and those of element $M$ occupy $2/3$ of the tetrahedral voids of the $hcp$ structure. The formula of the binary compound is

Which of the following is not a Lewis acid?

If $P=(0,1,0)$ and $Q=(0,0,1)$, then the length of the projection of the line segment $PQ$ on the plane $x+y+z=3$ is

The Henry's law constant for the solubility of $N_2$ gas in water at $298 \ K$ is $1.0 \times 10^5 \ atm$. The mole fraction of $N_2$ in air is $0.8$. The number of moles of $N_2$ from air dissolved in $10 \ moles$ of water at $298 \ K$ and $5 \ atm$ pressure is

$A$ particle is suspended from a vertical spring which is executing $S.H.M.$ of frequency $5 \ Hz$. The spring is unstretched at the highest point of oscillation. What is the maximum speed of the particle? (Take $g = 10 \ m/s^2$)

$A$ thin metallic spherical shell contains a charge $Q$ on it. $A$ point charge $+q$ is placed at the centre of the shell and another charge $q'$ is placed outside it as shown in the figure. All the three charges are positive. The force on the charge at the centre is: