'Mottled chlorosis' on the leaves occurs due to the deficiency of

Deficiency of which element causes deficiency of nitrogen?

Heart rot of marigold is caused by the deficiency of

The deficiency of which mineral element leads to the cessation of the repair process in aging cells?

Plants grow in a magnesium-deficient soil,but what happens if urea is added to the soil?

$A$: 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.