Which of the following is not caused by the deficiency of mineral nutrition?

Death of leaf tissues in plants is caused by the deficiency of:

In a $Citrus$ plantation,all the plants were found to be suffering from the die-back disease,and spraying of fungicides was of no help. This problem was due to the deficiency of:

Assertion : Deficiency of sulphur causes chlorosis in plants.
Reason : Sulphur is a constituent of chlorophyll,protein and nucleic acids.

$A$: Manganese toxicity causes brown spots,chlorotic veins,and inhibition of calcium translocation to the shoot apex.
$R$: Toxic effects may be due to direct excess of micronutrients or their interference in the absorption and functioning of other nutrients.

Interveinal chlorosis of leaves is caused by the deficiency of