Photosynthetically active radiation is:

The correct answer is Option (2) → Part of incident solar radiations.

Option (1) Incident solar radiations. — Incorrect. Incident solar radiation is all the sunlight falling on the plant. NCERT says less than 50 per cent of it is PAR, so PAR is only a part of it, not the whole.

Option (2) Part of incident solar radiations. — Correct. Photosynthetically active radiation (PAR) is the part of the incident solar radiation that plants can use for photosynthesis. It is less than 50 per cent of the sunlight reaching the plant.

Option (3) Green and Yellow light of visible spectrum only. — Incorrect. PAR covers the visible light used in photosynthesis, not only green and yellow.

Option (4) All radiations that are allowed by ozone through stratosphere to reach earth's surface. — Incorrect. It is a part of the radiation reaching the plants, not all of it.

NCERT Extract:
Energy Flow – “Except for the deep sea hydro-thermal ecosystem, sun is the only source of energy for all ecosystems on Earth. Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR). We know that plants and photosynthetic bacteria (autotrophs), fix Sun’s radiant energy to make food from simple inorganic materials.”