1,their non-metallic property increase numerically
2,their atom size decrease from sodium to chlorine
3,Q is the Al which form Al2O3 with oxygen.It is an amphoteric oxide.
4Al+3O2==2Al2O3 Al2O3+6HCl=AlCl3+3H2O Al2O3+NaOH==NaAlO2+H2O
R is an non-metallic atom so that it may form a oxide that will solute in alkali.So it may be the SiO2.So R is Si.
SiO2+2NaOH==Na2SiO3+H2O