As evaporation has a cooling effect, the rate at which the liquid cools down due to evaporation is equal to the rate at which heat is added to the container, keeping the liquid temperature constant.
Because the subscripts are what identify the compound. Changing the coefficient is okay, since you are only changing the number of whole compounds. If you change the subscript, however, you will change the compound into a completely different one. Hope that helps!!
You did not add the answers, but a non-living factor that could contribute could be temperature.
Answer : The concentration of the sodium hydroxide solution is, 0.521 M
Explanation :
To calculate the concentration of base, we use the equation given by neutralization reaction:

where,
are the n-factor, molarity and volume of acid which is 
are the n-factor, molarity and volume of base which is NaOH.
We are given:

Putting values in above equation, we get:

Thus, the concentration of the sodium hydroxide solution is, 0.521 M