Which one of the following elements in plants is not remobilised?

Elements that are actively mobilised within the plant are exported from older, senescing leaves to young tissues; their deficiency symptoms appear first in older leaves. Examples: nitrogen, phosphorus, potassium and magnesium.
Elements that are relatively immobile are not transported out of mature organs; their deficiency symptoms appear first in young tissues.
Calcium is a part of the structural component of the cell (calcium pectate of the middle lamella) and hence is not easily released.
Sulphur is only slowly mobile, but calcium is the classic example of an element that is not remobilised.
Hence the element not remobilised is calcium.