Ex-situ conservation includes:

The correct answer is Option (4) → seed banks

Option (1) biosphere reserves — Incorrect. A biosphere reserve is a large protected area where the whole ecosystem is conserved. The species stay in their natural habitat, so this is in situ conservation.

Option (2) national parks — Incorrect. A national park protects animals and plants where they live naturally. It is a protected area and so a method of in situ conservation.

Option (3) wildlife sanctuaries — Incorrect. A wildlife sanctuary is also a protected natural area. The wild animals are protected in their own habitat, which is in situ conservation.

Option (4) seed banks — Correct. In a seed bank, seeds are kept away from the natural habitat, for long periods, so that the plant can be grown again later. This is ex situ (off-site) conservation, like zoological parks and botanical gardens.

NCERT Extract:
How Do We Conserve Biodiversity? – “… Ex situ Conservation– In this approach, threatened animals and plants are taken out from their natural habitat and placed in special setting where they can be protected and given special care. Zoological parks, botanical gardens and wildlife safari parks serve this purpose. There are many animals that have become extinct in the wild but continue to be maintained in zoological parks. In recent years ex situ conservation has advanced beyond keeping threatened species in enclosures. Now gametes of threatened species can be preserved in viable and fertile condition for long periods using cryopreservation techniques, eggs can be fertilised in vitro, and plants can be propagated using tissue culture methods. Seeds of different genetic strains of commercially important plants can be kept for long periods in seed banks.”