Final answer:
For large alkyl group substituents on an aromatic ring, the most favorable future substitution position tends to be the para position, as it minimizes steric hindrance.
Step-by-step explanation:
If the alkyl group substituent on the aromatic ring is large, the most favorable position for future substitution tends to be the para position (C). Larger alkyl groups can cause steric hindrance, which is reduced when groups are on opposite sides of the benzene ring as in para positioning. The ortho position (A) puts substituents next to each other, leading to significant steric hindrance with large groups. The meta position (B) is less hindered than ortho but more so than para. There is no 'iso' position in this context, so option (D) is not applicable.