Forest, grassland and desert are examples of:

The correct answer is Option (2) → Terrestrial ecosystem

Option (2) Terrestrial ecosystem — Correct. Ecosystems are of two kinds: terrestrial (on land) and aquatic (in water). Forest, grassland and desert are all on land, so they are examples of terrestrial ecosystems; pond, lake and river are aquatic.

NCERT Extract:
Ecosystem – “… Ecosystem varies greatly in size from a small pond to a large forest or a sea. Many ecologists regard the entire biosphere as a global ecosystem, as a composite of all local ecosystems on Earth. Since this system is too much big and complex to be studied at one time, it is convenient to divide it into two basic categories, namely terrestrial and aquatic. Forest, grassland and desert are some examples of terrestrial ecosystems; pond, lake, wetland, river and estuary are some examples of aquatic ecosystems.”