Q.What is the action of conc. HI with glucose ?

When glucose cyclises to its ring (pyranose/furanose) form, a new stereocentre is created at C-1; the two possible configurations at just this one carbon give rise to $\alpha$- and $\beta$-D-glucose, a relationship specifically called anomerism.

When the open-chain form of D-glucose cyclises (the $-OH$ at C-5 attacking the aldehyde carbon, C-1), a new asymmetric (stereogenic) carbon is created at C-1, called the anomeric carbon. Depending on the spatial orientation of the newly formed $-OH$ group at this carbon (relative to the reference $-CH_2OH$ group at C-5), two distinct cyclic forms result: $\alpha$-D(+)-glucose (with the C-1 $-OH$ on the opposite side to the reference group) and $\beta$-D(+)-glucose (same side). Since these two forms differ in configuration at only this one carbon (the anomeric carbon) while all other stereocentres remain identical, they are called anomers — a special sub-class of diastereomers (epimers differ at any single stereocentre in general, b …