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

Step 1: Defining Meta-Directing Groups Meta-directing groups are those that deactivate the $o/p$ positions by withdrawing electron density via resonance ($-R$ effect).

Step 2: Analyzing the Sets

• Set C: $\ce{-NO2}$ (Nitro), $\ce{-CHO}$ (Aldehyde), $\ce{-SO3H}$ (Sulfonic acid), $\ce{-COR}$ (Ketone). All are strongly electron-withdrawing and meta-directing.
• Other sets contain activating groups like $\ce{-NH2}$ or $\ce{-OCH3}$ which are $o/p$ directing.

$\boxed{\text{Answer: (c)}}$