The anode voltage of a photocell is kept fixed. The wavelength $\lambda$ of the light falling on the cathode is gradually changed. The plate current $I$ of the photocell varies as follows:

$A$ coil of $50$ turns and $4$ cm radius carries $2$ $A$ current. The magnetic field at its centre is ...... mT.

Which cell organelle can be identified by Sudan Black?

In the following sequence of reactions,the alkene affords the compound $B$:
$CH_3-CH=CH-CH_3$ $\xrightarrow{O_3} A$ $\xrightarrow{Zn, H_2O} B$
The compound $B$ is

The formation of the oxide ion $O^{2-}_{(g)}$ requires first an exothermic and then an endothermic step as shown below:
$O_{(g)} + e^- \rightarrow O^{-}_{(g)}$; $\Delta H_{eg} = -142 \ kJ \ mol^{-1}$
$O^{-}_{(g)} + e^- \rightarrow O^{2-}_{(g)}$; $\Delta H_{eg} = +844 \ kJ \ mol^{-1}$
This is because:

$Assertion (A)$: van der Waals' forces are responsible for chemisorption. $Reason (R)$: High temperature is favourable for chemisorption. The correct answer is