Choose the grammatically correct sentence:

The correct answer is Option (3) → Please set the flower vase on the middle shelf of the cupboard.

“Set” and “lay” take an object, “sit” and “lie” do not:

• “Set” means to put something in a place. It takes an object: it acts on something. Its forms are set – set – set.
• “Lay” (lay – laid – laid) also takes an object. “Sit” (sit – sat – sat) and “lie” (lie – lay – lain) take no object.
• Here “set” acts on the object “the flower vase”. So the sentence is right.

Why the Other Options are Incorrect?

Option 1: The tired dog laid in the shade of the jamun tree for the whole afternoon. — Incorrect. The given sentence says “the dog laid”. The dog is not putting anything down, so the verb has no object. The verb with no object is “lie”, and its simple past (V2) is “lay”.
Corrected: The tired dog lay in the shade of the jamun tree for the whole afternoon.

Option 2: Grandfather has lain his reading glasses somewhere and cannot find them. — Incorrect. The given sentence says “has lain his reading glasses”. The verb acts on an object, “his reading glasses”, so the verb is “lay”. Its past participle (V3) after “has” is “laid”.
Corrected: Grandfather has laid his reading glasses somewhere and cannot find them.

Option 4: The guests were asked to set on the mats for the wedding lunch. — Incorrect. The given sentence says “to set on the mats”. The guests are not putting anything down. They take a seat, so the verb with no object, “sit”, is needed.
Corrected: The guests were asked to sit on the mats for the wedding lunch.