Among animals, which taxonomic group is the most species-rich?

The correct answer is Option (4) → Insects

Among animals, insects are the most species-rich taxonomic group. They make up more than 70 per cent of all animal species recorded, so out of every 10 animals on the planet, 7 are insects. Mammals, fishes and reptiles are far smaller groups; in fact, the fungi alone have more species than fishes, amphibians, reptiles and mammals combined. Figure 13.1 shows insects filling most of the invertebrate circle.

NCERT Extract:
How Many Species are there on Earth and How Many in India? – “… More than 70 per cent of all the species recorded are animals, while plants (including algae, fungi, bryophytes, gymnosperms and angiosperms) comprise no more than 22 per cent of the total. Among animals, insects are the most species-rich taxonomic group, making up more than 70 per cent of the total. That means, out of every 10 animals on this planet, 7 are insects. Again, how do we explain this enormous diversification of insects?”

Figure 13.1 Representing global biodiversity: proportionate number of species of major taxa of plants, invertebrates and vertebrates