An open vessel at $300 \ K$ is heated until $2/5$ of the air in it has been expelled. Assuming the volume of the vessel remains constant,find the temperature to which the vessel has been heated in $K$.

Boron halides behave as Lewis acids because of their nature.

The bob of a simple pendulum is hanging vertically down from a fixed identical bob by means of a string of length $l$. If both bobs are charged with a charge $q$ each,what is the time period of the pendulum? (Ignore the radii of the bobs.)

If the functions $f$ and $g$ are defined by $f(x) = 3x - 4$ and $g(x) = 2 + 3x$ for $x \in R$, then $g^{-1}(f^{-1}(5))$ is equal to

The number of ways that $8$ beads of different colours can be strung as a necklace is

If the circle $x^2+y^2+6x-2y+k=0$ bisects the circumference of the circle $x^2+y^2+2x-6y-15=0$,then $k$ is equal to