What is the common name of ${\mathrm{CH}}_3\mathrm{COOH}$?

Which two of the following compounds could belong to the same homologous series

 $\left(\mathrm{a}\right){\mathrm{C}}_2{\mathrm{H}}_6{\mathrm{O}}_2,\left(\mathrm{b}\right) {\mathrm{CH}}_4\mathrm{O},\left(\mathrm{c}\right) {\mathrm{C}}_2{\mathrm{H}}_6\mathrm{O}, \left(\mathrm{d}\right) {\mathrm{C}}_2{\mathrm{H}}_6$ 

Name the classes of organic compounds represented by the following formulae:
(i) ${\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{NH}}_2$
(ii)