Acid Anhydrides

Which of the following will not yield an acid anhydride?

Identify $\mathrm{Z}$ in the following reaction sequence:

${\mathrm{CH}}_3\mathrm{CHO}\underset{\mathrm{Dilute} {\mathrm{H}}_2{\mathrm{SO}}_4}{\overset{{\mathrm{MnO}}_4^{-}}{\to }}\mathrm{X}\stackrel{{\mathrm{SOCl}}_2}{\to }\mathrm{Y}\underset{∆}{\overset{{\mathrm{CH}}_3\mathrm{COONa}}{\to }}\mathrm{Z}$

Identify $\mathrm{Z}$ in the following reaction sequence:

${\mathrm{CH}}_3\mathrm{CHO}\underset{\mathrm{Di}l {\mathrm{H}}_2{\mathrm{SO}}_4}{\overset{{\mathrm{MnO}}_4^{-}}{\to }} \mathrm{X}\stackrel{{\mathrm{SOCI}}_2}{\to }\mathrm{Y}\underset{\mathrm{\Delta }}{\overset{{\mathrm{CH}}_3\mathrm{COONa}}{\to }}\mathrm{Z}$

Which of the two acids form anhydrides on heating?
($\mathrm{I}$) Oxalic acid
($\mathrm{II}$) Succinic acid
($\mathrm{III}$) Benzoic acid
($\mathrm{IV}$) Phthalic acid