Hydro Bomb (sometimes listed as Hydrogen/Hydra Bomb or Hydro-bomb) is a small bomb/atom-type firecracker made for a loud single blast — primarily a daytime/loud-bang cracker. 
Usually sold in boxes/pockets of 10 pieces (10 pcs per packet is the common retail unit).
Retail listings commonly show ≈ ₹60–₹80 per box (10 pcs) in current online shop listings; prices vary by seller, discounts, and minimum-order rules. Wholesale/discounted rates can be lower per box.