Which element(s) are highly mobile in plants?
1. N
2. P
3. Ca
4. K
Options:

Correct option is D

Highly mobile elements in plants include:
N (Nitrogen)
P (Phosphorus)
K (Potassium)
These elements can be remobilized from older to younger tissues during nutrient deficiency. Calcium (Ca) is immobile because it gets fixed in plant structures. So, the correct set is: 1, 2, 4