Select the most appropriate option that can substitute the underlined segment in the given sentence. If there is no need to substitute it, select ‘No substitution’.

This is the group of leaders in whom the ruling government has placed its trust.

To determine the most appropriate option to substitute the underlined segment "in whom the ruling government", let's analyze the grammatical structure of the sentence:

Sentence: "This is the group of leaders in whom the ruling government has placed its trust."

1. Analyzing the preposition and pronoun: The verb phrase in the relative clause is "has placed its trust". The standard idiom is to "place one's trust in someone". Therefore, the preposition "in" is grammatically correct.
2. Choosing between "who" and "whom": The pronoun refers to the "group of leaders", which is the object of the preposition "in". In English grammar, "whom" is the objective case pronoun, whereas "who" is the subjective case pronoun. Since it follows the preposition "in" and acts as its object (i.e., "placed its trust in them"), the objective pronoun "whom" must be used.
3. Evaluating the options:
- "in who the ruling government": Incorrect because "who" is subjective instead of objective "whom".
- "with who the ruling government": Incorrect because the idiom is "trust in", not "trust with" in this context, and it uses "who" instead of "whom".
- "on who the ruling government": Incorrect because the preposition "on" is incorrect for this idiom, and it uses "who".
- "no substitution": Correct, because "in whom" is grammatically precise and idiomatic.

Therefore, the sentence is already correct as written, and no substitution is needed.