Crotonyl alcohol is an example of

Observe the following statements :
$I$. Bleaching powder is used in the preparation of chloroform.
$II$. Bleaching powder decomposes in the presence of $CoCl_2$ to liberate $O_2$.
$III$. Aqueous $KHF_2$ is used in the preparation of fluorine.
The correct combination is :

Which of the following compounds will absorb the maximum quantity of heat when dissolved completely in the same amount of water? The heats of solution of these compounds at $25 \ ^\circ C$ in $kJ/mole$ of each solute is given in brackets.

In the context of the lanthanoids,which of the following statements is not correct?

What is the mixture of $MgCl_2$ and $MgO$ called?

$\sqrt{10 - \sqrt{24} - \sqrt{40} + \sqrt{60}} = ?$