Explanation:

Let’s break it down one by one:

- Option 1: Ethrel

Ethrel (also called ethephon) is used to release ethylene gas. It’s often applied to crops like pineapples for flowering or to speed up fruit ripening—not really for breaking potato dormancy.

- Option 2: Thiourea

This is the main chemical used to break dormancy in seed potatoes. Thiourea helps sprout eyes on the potato tuber much faster by interfering with natural dormancy signals.

- Option 3: Indole acetic acid

This is a type of auxin, basically a plant growth hormone that mainly helps with root formation. There’s no major role here in breaking potato dormancy.

- Option 4: Napthalene acetic acid

Another synthetic auxin—its main gigs are controlling fruit drop and boosting root growth. Again, not used for getting potato tubers to sprout.

So, what this really means is: the correct answer is Option 2 – Thiourea.