Magnesium deficiency shows chlorosis first in:
Correct option is B, Older leaves. In MINERAL Transport problems like this, the accurate statement is Older leaves; the others are common mix-ups. Not these: A) Young leaves; C) Roots; D) Flowers. Tissue transport questions usually turn on xylem vs phloem, living vs dead cells, or source vs sink.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.