Match the following:

Compound	Uses
$1$. Soda ash	$a$. In purification of sugar
$2$. Calcium oxide	$b$. As an antacid
$3$. Baking soda	$c$. In paper and textile industries
	$d$. To prepare pure fats and oils

Assertion : Potassium and caesium are used in photoelectric cells.
Reason : Potassium and caesium emit electrons on exposure to light.

Statement $A$: Extraction of magnesium is done by the electrolysis of a molten mixture of $MgCl_2$,$NaCl$,and $CaCl_2$.
Reason $R$: Calcium chloride acts as a reducing agent.

Given below are two statements,one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: The alkali metals and their salts impart characteristic colour to reducing flame.
Reason $R$: Alkali metals can be detected using flame tests.
In the light of the above statements,choose the most appropriate answer from the options given below.

The correct order of solubility for the given compounds is:

To which group do the following elements belong? Which of them has the highest metallic character?
$K, Na, Li, Rb$