Two samples A and B contain equal amount of radioactive substances. If $\left(\dfrac{1}{8}\right)^{th}$ of sample A and $\left(\dfrac{1}{128}\right)^{th}$ of sample B, remain after 9 hours, then the ratio of half life period of B to that of A is

In an NPN transistor, the collector current is 28 mA. If 80% electrons reach the collector, its base current in mA is

The output Y of the given logic circuit is

For intrinsic semiconductor, if $n_h$ and $n_e$ represent the number of holes per unit volume and the number of free electrons per unit volume respectively then