Which is not correctly matched? 
(1) Basic strength ${\mathrm{Cs}}_2\mathrm{O}<{\mathrm{Rb}}_2\mathrm{O}<{\mathrm{K}}_2\mathrm{O}<{\mathrm{Na}}_2\mathrm{O}<{\mathrm{Li}}_2\mathrm{O}\text{ of }$ oxides 
(2) stability of ${\mathrm{Na}}_2{\mathrm{O}}_2<{\mathrm{K}}_2{\mathrm{O}}_2<{\mathrm{Rb}}_2{\mathrm{O}}_2<{\mathrm{Cs}}_2{\mathrm{O}}_2$ peroxides
(3) Stability of ${\mathrm{LiHCO}}_3<{\mathrm{NaHCO}}_3<{\mathrm{KHCO}}_3$ $<{\mathrm{RbHCO}}_3<{\mathrm{CsHCO}}_3$
(4) Melting point $\mathrm{NaF}<\mathrm{NaCl}<\mathrm{NaBr}<\mathrm{Nal}$

Basic strength of the oxides increase in the order ${\mathrm{Li}}_2\mathrm{O}<{\mathrm{Na}}_2\mathrm{O}<{\mathrm{K}}_2\mathrm{O}<{\mathrm{Rb}}_2\mathrm{O}<{\mathrm{Cs}}_2\mathrm{O}$ The increase in basic strength is due to the decrease in I.E. and increase in electropositive character. The melting points of the halides decrease in the order NaF > NaCl > NaBr > Nal, as the size of the halide ion increases. The decrease in melting point is due to increase in the covalent character with increase in the size of anion according to Fajan's rule.