In one H₂O molecule, there are two hydrogen atoms along with one oxygen atom. So for every 1 oxygen atom (of which there are 2 of in an oxygen gas molecule) there needs to be 2 hydrogen atoms per oxygen( which in the equation of 2H2 +O2–> 2H2, that 2 H2 is broken down into 4 hydrogen atoms which means 2 hydrogen atoms have to bond to 1 oxygen atom and with 4 hydrogen atoms, there will be 2 atoms of oxygen which creates 2 molecules of water.
So to solve the question,
10.5g/2=5.25g of oxygen required to fully react with hydrogen to make water
Ionic compounds are compounds that are formed together by a cation and an anion. A cation is an ion with a positive charge. For example, Na+ and Ca2+. An ion has a negative charge, like Cl- and OH-. There is a greater chance of forming an ionic compound when they have a great difference in electronegativity, the ability to attract electrons toward itself. In the periodic table, elements that are opposite to each other, more likely found in opposite sides, would be more apt to form an ionic compound. Example would be NaCl and CaCl2 or Ca(OH)2.