Which of the following treatment will convert starch directly into glucose?

Fermentation by diastase will convert starch into maltose but not into glucose.

Zymase does not effect starch.

Further, dilute NaOH will not hydrolyse starch because the various glucose units in it are linked to each other by glycosidic (ether) linkage which are resistant to hydrolysis by NaOH. Thus only dilute ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4$ will hydrolyse starch into glucose.

$\underset{\mathrm{S}\mathrm{t}\mathrm{a}\mathrm{r}\mathrm{c}\mathrm{h}}{{\left({\mathrm{C}}_6{\mathrm{H}}_{10}{\mathrm{O}}_5\right)}_x}\underset{\mathrm{e}\mathrm{n}\mathrm{z}\mathrm{y}\mathrm{m}\mathrm{e}\mathrm{s}}{\stackrel{\hspace{1em}\mathrm{n}{\mathrm{H}}_2\mathrm{O}\hspace{1em}}{\to }}\underset{\text{Glucose}}{{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6}$