Within two hours of the incident, a team of police from the Metropolitan Police Crime Division arrested Munna, who had his hands burnt by acid.
The woman has received burn injuries on her face and neck, Dr Vineet Sachan at the district hospital said.
An 80-year-old woman allegedly poured acid on her relative, a 55-year-old woman, after a petty quarrel at Kangeyampalayam village near Sulur in the district on Saturday morning.
Three class 10 girl students and a boy of class 9 suffered minor burns, police said, adding the attacker fled the spot after the incident.
Rohit Yadav, 24, got burn injuries on his nape, back, chest and left shoulder during the acid attack in Godamau village under jurisdiction of Morawan police station.
However, what is even more appalling is that the attack committed by the classmate took place when a group of students were cleaning the toilet of the school on the orders of the teachers.
The woman suffered injuries and was sent home after primary medical aid at the district hospital.
Police said that the acid splashed on three women, including two married women who sustained minor injuries and the 13-year-old girl named Gungun Sonkar.
The police have obtained CCTV footage which is not clear. Efforts are on to nab the accused and personal rivalry could be a reason behind the crime, the police officer added.
Kerala witnessed 13 out of 252 acid attack incidents in the country. Uttar Pradesh topped the chart with 60 cases, while West Bengal is just behind with 54.