Which of the following mineral deficiencies will cause death of stem and root tips?

How are the terms 'critical concentration' and 'deficient' different from each other in terms of the concentration of an essential element in plants? Can you find the values of 'critical concentration' and 'deficient' for minerals $Fe$ and $Zn$?

Explain the terms chlorosis and necrosis.

Deficiency symptoms of mineral elements appear first in young leaves. - $P$
Deficiency symptoms of mineral elements appear first in senescent (older) leaves. - $Q$
$P$ and $Q$ are respectively:

It is observed that the deficiency of a particular element shows its symptoms initially in older leaves and then in younger leaves. How is the aspect of mobility of elements important to horticulture and agriculture?

On the basis of symptoms of chlorosis in leaves,a student inferred that this was due to the deficiency of nitrogen. This inference could be correct only if yellowing of leaves appeared first in