In the given compound, the electrophile attack will be favoured at

The correct answer is S.

To determine the site most favored for electrophilic attack, we analyze the electronic and steric factors in the given compound, N-phenylbenzamide (benzanilide):

1. Analysis of the Left Benzene Ring (Positions P and Q):
The left benzene ring is directly attached to the carbonyl carbon of the amide group ($-C=O$). The carbonyl group is highly electron-withdrawing due to resonance (-M effect) and induction (-I effect). This decreases the electron density of the left benzene ring, making it deactivated toward electrophilic aromatic substitution.

2. Analysis of the Right Benzene Ring (Positions R and S):
The right benzene ring is directly attached to the nitrogen atom of the amide group ($-\ddot{N}H-$). The nitrogen atom carries a lone pair of electrons that can be delocalized into the aromatic ring. This +M resonance effect significantly increases the electron density of the right benzene ring, activating it toward electrophilic attack.

3. Regioselectivity (Ortho vs. Para):
Since the right ring is activated and the left ring is deactivated, the electrophile will selectively attack the right ring. The nitrogen atom directs incoming electrophiles to the ortho and para positions:
- Position R represents the ortho position, which is sterically hindered by the bulky benzamido group linked to the nitrogen.
- Position S represents the para position, which is sterically unhindered and experiences strong electron-donating activation from the nitrogen lone pair.

Therefore, the electrophilic attack will be most favored at the para position, which is labeled as S.