Answer:
4. dangling modifier
Step-by-step explanation:
A dangling modifier refers to a word or phrase that is too distant from the word it intends to modify - which causes ambiguity - or that does not possess any word to modify at all. As a result, the expression when an old woman should be closer to the noun it modifies, which is Mrs. Jones. Thus, the revised sentence is:
The boy visited Mrs. Jones in the nursing home when she was an old woman.