The coefficients : a. 1,2,1,2
Further explanation
Given
Reaction(unbalanced)
CH4 +O2 -------» CO2 + H2O
Required
The blanced equation
Solution
Give a coefficient
CH4 +aO2 -------» bCO2 + cH2O
Make an equation
C, left=1, right=b⇒b=1
H, left=4, right = 2c⇒2c=4⇒c=2
O, left=2a, right=2b+c⇒2a=2b+c⇒2a=2.1+2⇒a=2
The equation becomes :
CH4 +2O2 -------» CO2 + 2H2O