The incident took place in the Kalindi Vihar colony of Trans-Yamuna area Friday.
Etmauddaula police station officers said Manish Jain forcibly entered the house of his neighbour and threw three crude bombs. One did not explode while the two others seriously injured the mother and daughter.
The victims are struggling for life at S.N. Medical College's emergency ward. The bomb hit 23-year-old Kavita Sharma on her abdomen and badly burnt her body.
Neighbours told the police that the boy was madly in love with Kavita and having failed to get any response resorted to the act. Police late night arrested the boy.
Deputy Inspector General Aseem Arun and other senior officials reached the site and ordered inquiry.
A case has been registered on the complaint lodged by the mother Rajeshwari.
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