The set of meta directing functional groups from the following sets is:

We need to identify the set containing only meta-directing functional groups in electrophilic aromatic substitution.

Key concept: Meta-directing groups are electron-withdrawing groups (EWGs) that deactivate the ring. They include: $$-NO_2$$, $$-CHO$$, $$-COR$$, $$-COOH$$, $$-COOR$$, $$-SO_3H$$, $$-CN$$, $$-CF_3$$.

Ortho/para-directing groups include: $$-NH_2$$, $$-NHR$$, $$-OH$$, $$-OCH_3$$, $$-NHCOCH_3$$, halogens.

Option A: $$-CN, -NH_2, -NHR, -OCH_3$$

$$-NH_2$$, $$-NHR$$, $$-OCH_3$$ are ortho/para directors. Not all meta.

Option B: $$-NO_2, -NH_2, -COOH, -COOR$$

$$-NH_2$$ is an ortho/para director. Not all meta.

Option C: $$-NO_2, -CHO, -SO_3H, -COR$$

All four are electron-withdrawing, meta-directing groups. All meta.

Option D: $$-CN, -CHO, -NHCOCH_3, -COOR$$

$$-NHCOCH_3$$ (acetamido group) is an ortho/para director despite being a weaker activator. Not all meta.

The correct answer is Option C) $$-NO_2, -CHO, -SO_3H, -COR$$.