Identify the basic oxide from the following.

List-$I$ Elements	List-$II$ Colour imparted to the flame
$A$. $K$	$i$. Violet
$B$. $Ca$	$ii$. Brick Red
$C$. $Sr$	$iii$. Crimson Red
$D$. $Ba$	$iv$. Apple Green

Choose the correct answer from the options given below:

Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$ :- Sodium is about $30$ times as abundant as potassium in the oceans.
Reason $R$ :- Potassium is bigger in size than sodium.
In the light of the above statements,choose the correct answer from the options given below:

Which of the following is not a product,when $RbO_2$ reacts with $H_2O$?

$A$ metal $(A)$ on heating in nitrogen gas gives compound $(B)$. $(B)$ on treatment with $H_{2}O$ gives a colourless gas which when passed through $CuSO_{4}$ solution gives a dark blue-violet coloured solution. $(A)$ and $(B)$ respectively,are

The electronic configuration of a metal is $1s^2 2s^2 2p^6 3s^1$. The formula of its oxide is: