The alum used for purifying water is

The formation of $Al_2O_3$ is accompanied by the release of a large amount of energy. This property is utilized in which of the following?

When borax is dissolved in water, the product formed is

Identify the correct statements about the anomalous behaviour of Boron:
$I$. Boron trihalides can form dimeric structures.
$II$. Boron shows $+1$ as a stable oxidation state.
$III$. Maximum covalency of Boron is four.
$IV$. Boron does not form $BF_{6}^{3-}$ ion.

Which one of the following forms a basic oxide?

Match the List-$I$ with List-$II$.

List-$I$ (Element)	List-$II$ (Application)
$A$. $Cs$	$I$. High temperature thermometer
$B$. $Ga$	$II$. Water repellent sprays
$C$. $B$	$III$. Photoelectric cells
$D$. $Si$	$IV$. Bullet proof vest

Choose the most appropriate answer from the options given below: