G'day love! An elements atomic number is the amount of protons in an element!
This is an incomplete question, here is a complete question.
Calculate the solubility of each of the following compounds in moles per liter. Ignore any acid-base properties.
CaCO₃, Ksp = 8.7 × 10⁻⁹
Answer : The solubility of CaCO₃ is, 
Explanation :
As we know that CaCO₃ dissociates to give
ion and
ion.
The solubility equilibrium reaction will be:

The expression for solubility constant for this reaction will be,
![K_{sp}=[Ca^{2+}][CO_3^{2-}]](https://tex.z-dn.net/?f=K_%7Bsp%7D%3D%5BCa%5E%7B2%2B%7D%5D%5BCO_3%5E%7B2-%7D%5D)
Let solubility of CaCO₃ be, 's'




Therefore, the solubility of CaCO₃ is, 
What do you mean by that Oh wait do you mean like 2×2=4 or 2+2=4 something like that maby?? I am still confused?? XD
Answer:
Number of moles of methane form = 2.3 mol
Explanation:
Given data:
Number of moles of Hydrogen = 4.6 mol
Number of moles of methane form = ?
Solution:
Chemical equation:
C + 2H₂ → CH₄
Now we will compare the moles of methane with hydrogen from balance chemical equation.
H₂ : CH₄
2 : 1
4.6 : 1/2×4.6 = 2.3 mol
Form 3.6 moles of hydrogen 2.3 moles of methane can be formed.