The balanced reaction that describes the reaction between methane and oxygen to produce water and carbon dioxide is expressed CH4 + 2 O2 = CO2 +2H2O. Hence for 2 moles of methane used, 4 moles of oxygen are needed to react completely.
The amount of fat will affect its melting point
Answer: The hydroxide concentration of this sample is 
Explanation:
When an expression is formed by taking the product of concentration of ions raised to the power of their stoichiometric coefficients in the solution of a salt is known as ionic product.
The ionic product for water is written as:
![K_w=[H^+]\times [OH^-]](https://tex.z-dn.net/?f=K_w%3D%5BH%5E%2B%5D%5Ctimes%20%5BOH%5E-%5D)
![7.7\times 10^{-14}=[H^+]\times [OH^-]](https://tex.z-dn.net/?f=7.7%5Ctimes%2010%5E%7B-14%7D%3D%5BH%5E%2B%5D%5Ctimes%20%5BOH%5E-%5D)
As ![[H^+]=[OH^-]](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%3D%5BOH%5E-%5D)
![2[OH^-]=7.7\times 10^{-14}](https://tex.z-dn.net/?f=2%5BOH%5E-%5D%3D7.7%5Ctimes%2010%5E%7B-14%7D)
![[OH^-]=3.85\times 10^{-7}](https://tex.z-dn.net/?f=%5BOH%5E-%5D%3D3.85%5Ctimes%2010%5E%7B-7%7D)
Thus hydroxide concentration of this sample is 
~Hello there! ^_^
Your question: Why should we not throw water in petrol fire..?
Your answer: We should not throw water in the petrol fire because oil, petrol etc are a bit weightless than water so it continues to flow over the water.
Hope this helps!