Dieback in citrus and cracking of apple is due to the deficiency of

Correct option is B

Dieback in citrus and cracking of apple is due to the deficiency of copper
Zinc deficiency in apple trees manifests as "little leaf" and "rosetting"
Zinc deficiency in citrus, often manifesting as "mottle leaf" or "frenching,
Sulphur deficiency in citrus manifests as stunted growth, pale green to yellow leaves (chlorosis) starting on younger leaves, and potentially reduced fruit quality