In this section, each item consists of six sentences of a passage. The first and sixth sentences are given as SI and S6. The middle four sentences in each have been jumbled up and labelled as P, Q, R and S. You are required to find the proper sequence of the four sentences and mark your response accordingly.

S1: The process of dissolving an acid or a base in water is a highly exothermic one.
P:  Care must be taken while mixing concentrated nitric acid or sulphuric acid with water.
Q: The acid must always be added slowly to water with constant stirring.
R: If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns.
S: The glass container may also break due to excessive local heating. 
S6: So we have to take precautions.