The number of unpaired electrons in the $p$-subshell of oxygen atom is

Which of the following electronic configurations has the maximum energy?

The total spin of an iron $(Fe)$ atom is .......

The orbital with $4$ radial and $1$ angular nodes is

Assertion $(A)$: Atoms with completely filled and half-filled subshells are stable.
Reason $(R)$: Completely filled and half-filled subshells have symmetrical distribution of electrons and have maximum exchange energy.
The correct answer is:

Give the symbol of the element with the lowest atomic number that has three $2p$ electrons.