Alum (Patika in telugu) is good for lemon plants.
https://www.vedantu.com/chemistry/alum
Alum is an inorganic compound composed of Water molecules, Aluminum, other Metal than Aluminium, and Sulphates. Alum is a double salt in the hydrated form. Alum exists in different forms: Potash Alum, Soda Alum, ammonium Alum, and chrome Alum. The general chemical formula for Alum is XAl(SO4)2ยท12H2O.
Aluminium Sulphate Alum