Al2O3 has a higher melting point than Na2O. This is because the ionic bond between Al3+ ions and O2- ions is stronger than that between Na+ and O2-. The charge on the Al3+ ion is larger than that of the Na+ ion
Combustion means the burning of something. So in the given question, you could say, “In this question, combustion means the burning of methane”.
C. Grams per Cubic Centimeter
Answer:
249.94ppm
Explanation:
Given parameters:
Mass of Pb(NO₃)₂ = 0.025g
Mass of water = 100g
Unknown:
Concentration of solution in ppm = ?
Solution:
Concentration in parts per million gives the amount of solute found in a million units of the solution. They are desirable for expressing very small amount of solutes in a large solution. For example, the level of arsenic in the soil.
Concentration in ppm = 
A solution is made up of solute and solvent. The solvent here is water.
mass of solution = mass of solute + mass of solvent = 0.025 + 100 = 100.025g
Concentration in ppm =
= 249.94ppm