The leaves die out early is due to the deficiency of:

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Hint:(1) Essential nutrients are required by all plants for their normal functioning and growth and each plant has a particular definite range in which a particular nutrient is required by it. When the amount of nutrients falls outside this range, it leads to the decline in the health and growth of the plant.
(2) Each of the nutrients required by a plant has its own set of symptoms. The symptoms which are caused by nutrient deficiencies are mainly of five types: chlorosis, interveinal chlorosis, necrosis, stunted growth and purplish-red coloring. By diagnosing the symptoms, the particular nutrient deficiency can be identified.

Complete step by step answer:
Let us first understand some plant nutrient deficiency terms. The term chlorosis in plants refers to the general yellowing of the plant tissues due to the lack of chlorophyll. The chlorophyll is the green pigment in plants which is responsible for their green color. The term interveinal chlorosis refers to the yellowing of the leaves in between the veins with the veins remaining green. The term necrosis refers to the death of most of the plant tissues, it causes the tissues to first turn brown and then die. Purplish-red discoloration occurs when the level of the purple pigment anthocyanin is above normal. Stunted plant growth means the slow rate of plant growth and shorter height of the affected plants.
Now, let us consider the options given one by one and understand the symptoms.
Nitrogen deficiency generally leads to stunted plant growth due to the reduction in proteins and leaves turn pale yellow or light green in color due to chlorosis, especially on the lower or older leaves because nitrogen is transferred from older leaves to more important younger leaves. Nitrogen deficiency also causes leaves to prematurely fall off. Thus, leaves die out early.
Phosphorus deficiency leads to stunted growth and dark green coloring of leaves, especially on the lower leaves. The leaves may also acquire a purple discoloration and sometimes necrosis.
Potassium deficiency leads to yellowing of the lower or older leaves, but the symptoms are limited to one leaf or one section of the leaf or plant. Chlorosis occurs with scattered black or dark brown spots, spotting generally occurs along leaf margins and the chlorotic areas are defined by burning of leaf margins. No interveinal chlorosis occurs.
Iron deficiency affects newer or younger leaves and interveinal chlorosis occur along with chlorosis due to which yellowing occurs between leaf veins. There is sharp distinction between the chlorosis affected areas and the veins.
Thus, the option A is correct.
The possible causes of nitrogen deficiency in plants are: too little nitrogen or too much of other nutrients like zinc, potassium, manganese in the soil, high pH value of the root environment or high solubility of nitrogen due to which it can be easily washed out of the soil. Nitrogen deficiency can be prevented by the application of fertilizers which have high nitrogen content like ammonium phosphate, calcium ammonium nitrate etc.