Deficiency of . . . . . . causes death of shoot and root tips in plants.

Why is it that in certain plants deficiency symptoms appear first in younger parts of the plant,while in others they do so in mature organs?

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:

'Petiole crack' is caused by the deficiency of

In plants,where does chlorosis occur due to magnesium deficiency?

High fluoride concentration in plants typically results in necrosis or chlorosis in: