The number above the symbol is the atomic mass (or atomic weight). This is the total number of protons and neutrons in an atom. The number below the symbol is the atomic number and this reflects the number of protons in the nucleus of each element's atom. Every element has a unique atomic number.
The correct answer is elements in family 7 have similar properties because elements in the same group or family have the same number of valence electrons.
Reactant + reactant = product
C + O2 = CO2
carbon dioxide is what's being made is product
There are 2 Ca, 4 H (2*2) and 4 O (2+2) on the left hand side. So there should be the same number of atoms 2Ca and 4(O+H) on the right hand side. The reaction is a synthesis (making something new), rather than a decomposition (destroying something).
The answer is Two molecules of Ca(OH)2 should be produced during the synthesis reaction.
