*Q:19 Correct Answer* ✅ *(1) Both A and R are true and R is the correct explanation of A* > *Explanation:* Arthropoda is the largest phylum in the animal kingdom, including insects, crustaceans, arachnids, and more. Their extraordinary morphological diversity (variety in body structure, appendages, and adaptations) and ability to occupy nearly every ecological niche — from deep oceans to high mountains — explain their evolutionary success and abundance.