Explanation:

Let's break it down:

- Option 1: whoever

- "Whoever" is typically used in the nominative case, meaning it acts as the subject of a clause, which doesn’t fit well in this context.

- Option 2: which

- "Which" is used for things, not people. Since we're talking about "nobody," a person, this option is unsuitable.

- Option 3: whom

- "Whom" is used as the object of a verb or preposition, which fits perfectly here because it refers to confiding in someone.

- Option 4: whose

- "Whose" is a possessive form and doesn't fit in the context where a person to confide in is needed.