Questions

Given Equation is 

Mg + O2 → MgO

Balancing the Chemical Equation is nothing but Conservation of Matter. As Matter is Neither created nor Destroyed, it must be conserved.

Here we have 1 Mg and 2 O on the left side and 1 Mg and 1 O on the right side

To balance that, add 1 Mg on the left side so that it becomes 2 Mg and 2 O on the left side

i.e,

2 Mg + O2 → 2 MgO

Here it has 2 Mg & 2 O on the left side and 2 Mg and 2 O on the right side and the Chemical equation is Balanced.

The sentence is grammatically and contextually correct. ‘His’ is the correct form of pronoun to be used. Thus, the correct formation would be, ‘He reached his destination at night’.

As temperature of Leh will be lowest during winters from the given options, the highest pressure will be at Leh.