Which of the following is basic in nature?

$A$ point moves in the $xy$-plane such that the sum of its distances from two mutually perpendicular lines is always equal to $5$ units. The area (in sq units) enclosed by the locus of the point is

Which one of the following elements reduces $NaOH$ to $Na$?

Based on lattice energy and other considerations,which one of the following alkali metal chlorides is expected to have the highest melting point?

Two coaxial solenoids of different radii carry current $I$ in the same direction. Let $\vec{F}_1$ be the magnetic force on the inner solenoid due to the outer one and $\vec{F}_2$ be the magnetic force on the outer solenoid due to the inner one. Then:

Five elements $A, B, C, D$ and $E$ have work functions $1.2\, eV, 2.4\, eV, 3.6\, eV, 4.8\, eV$ and $6\, eV$ respectively. If light of wavelength $4000\, \mathring{A}$ is allowed to fall on these elements,then photoelectrons are emitted by