Hyperpolarization of guard cell membrane leads to influx of:
Go with C — K⁺. Under STOMATA MOVEMENT, 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) Na⁺; B) Ca²⁺; D) H⁺. 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.