A road tanker car

(a) To see if the river water contains some acid or not, the specialist can use a blue litmus paper. If the blue litmus paper changes to red, then it is confirmed that the river contains some acid and if the colour does not change, this means river does not contain any acid.

(b) Corroding is the right term instead of melting. Hence, the correct sentence is “At the side of the road, iron drain covers began corroding and fizzing as the acid ran over them.”

(c) Iron drain covers began fizzing because when acid ran over them reacts with iron; it releases hydrogen gas. Due to the formation of hydrogen gas, bubbles occur and this causes fixing of drain covers.