In a water culture experiment a plant showed poor growth and yellowing of the leaves. These symptoms were probably due to the absence of

The symptoms described in the question are typical of a nutrient deficiency, and the specific symptoms of poor growth and yellowing of leaves suggest that the plant may be deficient in an essential mineral nutrient. Among the options provided, calcium, phosphorus, iron, zinc, and copper are all essential mineral nutrients for plants. However, of these options, iron is most commonly associated with the symptoms described, as a lack of iron can result in yellowing of leaves due to a reduction in chlorophyll synthesis. This condition is known as iron chlorosis. Therefore, the most likely answer is iron.