Calcium deficiency is rare and often misdiagnosed. It is characterized by reduced chlorophyll, poor root formation, delayed maturity, and legumes and brassicas being particularly susceptible. Calcium is an essential nutrient for plants as it helps in cell wall formation, enzyme activation, and nutrient uptake. When there is a deficiency of calcium, these processes are disrupted, leading to the aforementioned symptoms. Therefore, calcium deficiency is the correct answer.