Identify the grammatically correct sentence from the options given:

The correct answer is Option (3) → Of all the students, Ananya is the most diligent.

An adjective is a word that describes a noun or a pronoun, for example a tall tree, the food is tasty.

Degrees of comparison:

• The comparative (taller, more diligent) compares two persons or things. The superlative (tallest, most diligent) picks one out of three or more.
• Short adjectives add -er / -est (large, larger, largest). Long adjectives such as diligent (hard-working) take more / most. The two are never used together.
• This sentence: "Of all the students" means a whole group, so the superlative "the most diligent" is correct.

Why the Other Options are Incorrect?

Option 1: Mount Everest is the most highest peak in the world. — Incorrect. "Most highest" is a double superlative. "Highest" is already the superlative.
Corrected: Mount Everest is the highest peak in the world.

Option 2: This is the more interesting of the novels. — Incorrect. "The more ... of" is used only when just two are compared (the more interesting of the two novels). "The novels" here means a group, so the superlative is needed.
Corrected: This is the most interesting of the novels.

Option 4: My house is more large than yours. — Incorrect. "Large" is a one-syllable adjective, so its comparative is "larger", not "more large".
Corrected: My house is larger than yours.

Contrast: two persons or things take the comparative, three or more the superlative. "More/most" is never added to an -er/-est form.