Explanation

(a)
Glucose reacts with acetic anhydride in the presence of anhydrous ${ZnCl}_{2}$ to form penta-acetyl glucose which indicates the presence of 5-OH groups in glucose molecule and the open chain structure of glucose.
$\ \ CHO\$
$\ \ \ |\ \$
$\ (CHOH)_{4} + \ 5\left( CH_{3}CO \right)_{2}O\ \underset{\mathrm{\Delta}}{\overset{\ \ \ \ \ ZnCl_{2}\ \ \ \ \ }{\rightarrow}}\ \$
$\ \ \ \ |\ \$
$\ \ \ CH_{2}OH\ \$
$\ glucose\$
$\ \ \ CHO\$
$\ \ \ |$
$\left( CHOCOCH_{3} \right)_{4} + \ 5CH_{3}COOH\$
$|\$
$\ \ \ CH_{2}OCOCH_{3}$
Pentaacetyl glucose