Answer: The correct option is 3.
Explanation: We are given a compound which is made up of iron and oxygen only. The ratio of the two are given as:

This means that, number of iron ions are 2
Number of oxide ions are 3
From the above information, the formula becomes : 
The valency of iron = 3
Valency of oxide = 2
This compound is named as iron (III) oxide.
Hence, the correct option is 3
Answer:
Q = -22.9 kJ
Explanation:
Given that,
Mass of water, m = 150.3 g
Water gets cool from 25.60°C to -10.70°C.
The specific heat of water, c = 4.2 J/g°C
The formula for heat needed is given by :

So, 22.9 kJ of heat is needed to be removed to cool.
Answer:
B 2Li + Cl2 ---> 2LiCl
Explanation:
There are 2 Li atoms and 2 Cl atoms on both sides of the equation.