When comparing two things, we use the comparative form of the adjective.
Difficult is a multi-syllable adjective, so its comparative form is more difficult.
The sentence compares this examination with the other examination, so the comparative is required.
Why the other options are incorrect:
❌ more easy → Incorrect. The correct comparative is easier, not more easy.
❌ difficult → Positive degree, not comparative.
❌ more easier → Double comparative. We use either easier or more difficult, not more easier.