Chemical Reactions And Equations PYQs — 3 UPSC CSE Previous Year Questions

Question 1

Which of the following is/are the example/examples of chemical change? Crystallization of sodium chloride Melting of ice Souring of milk Select the correct answer using the code given below.

Accepted Answer

B. 3 only

Question 2

Mixture of which one of the following pairs of gases is the cause of occurrence of mast of the explosions in mines?

Accepted Answer

C. Methane and air

Question 3

Match List-I (Oxidation number) with List II (The element) and select the correct answer using the codes given below the lists:

	List-I (Oxidation number)		List-II (The elements)
A.	2	1.	Oxidation number of Mn in MaO₂
B.	3	2.	Oxidation number of S in $H_{2} S_{5} O_{7}$
C.	4	3	Oxidation number of Ca in CaO
D.	6	4.	Oxidation number of Al in NaA1H₄

Codes:
ABCD

Accepted Answer

A. 3412