Mn toxicity develops deficiency symptoms of Ca, Mg and Fe because

Manganese toxicity leads to the appearance of brown spots surrounded by chlorotic veins.

Manganese competes with iron and magnesium for uptake from the soil and with magnesium for binding with enzymes.

Manganese also inhibits calcium translocation to the shoot apex.

Therefore, excess of manganese induces deficiencies of iron, magnesium, and calcium.

Answer: Mn competes with Fe, Mg for uptake and inhibits translocation of calcium.