The concentration of an essential element below which plant growth is retarded is termed as .......

$A$: 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.

Deficiency symptoms of an element tend to appear first in young leaves. It indicates that the element is relatively immobile. Which one of the following elemental deficiencies would show such symptoms?

Which of the following is deficient in the soil of Gujarat,$U$.$P$.,and Maharashtra in a large area?

Which mineral deficiency causes the 'Exanthema' disease in citrus plants?

'Petiole crack' is caused by the deficiency of