Tonicity of a solution refers to its ability to:
Go with B — Modify cell volume. Under BASICS of PLANT, this is the standard explanation you’d use in class: it names the real driver or definition, while the rest are nearby but wrong. Not these: A) Change temperature; C) Break cell wall; D) Alter metabolism. When two options sound similar, choose the one that matches the textbook definition most tightly.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.