Dieback disease in citrus plants is caused by the deficiency of which of the following elements?

Which of the following is the most common symptom of viral diseases in plants?

As per the prediction model for Indian stem rust disease, what will occur if the following conditions are met? 1. 5-6 infection sites are observed within 25 ± 5 km around January 15-20 in UP and North Bihar. 2. Rain amount and rainy days over Northwest India from January to mid-April are twice the normal level.