Which of the following sentences is correct ?

How to Determine which Sentence is Correct?

• The following are some verbs, nouns, and adjectives that are followed by a fixed preposition:
• Exonerate from, lean against, accuse someone of something, have a preference for, get a break from, be irritated by, etc.
• Example: I require a surface to rest my back on.
• After the verb lean, the preposition against must be used, in accordance with the norm and the example above.
• Leaning on something refers to sitting or standing while having a portion of your body resting against it.
• The fourth option will be the best one given the necessary framework.

Summary:

Which of the following sentences is correct? (a) The old man leaned to the wall. (b) The old man leaned in the wall. (c) The old man leaned the wall. (d) The old man leaned against the wall.

The old man leaned against the wall is the correct sentence. The concept to find the correct answer has been explained in this post above. Using the concept similar types of questions can be answered easily.