Among the following compounds $(I-III)$,the correct order of reactivity towards electrophilic substitution is:

$A$ metallic ring connected to a rod oscillates freely like a pendulum. If now a magnetic field is applied in a horizontal direction so that the pendulum now swings through the field,the pendulum will

The number of ways in which $6$ men and $5$ women can dine at a round table,if no two women are to sit together,is:

In the Young's double slit experiment using a monochromatic light of wavelength $\lambda$,the path difference (in terms of an integer $n$) corresponding to any point having half the peak intensity is:

Two bodies of masses $m$ and $4m$ are placed at a distance $r$. The gravitational potential at a point on the line joining them where the gravitational field is zero is

$A$ black body radiates energy at the rate of $E \text{ W/m}^2$ at a high temperature $T \text{ K}$. When the temperature is reduced to $\left(\frac{T}{2}\right) \text{ K}$,the radiant energy is