Explain why the addition of hydrogen cyanided to carbonyl compounds is accelerated by bases and retarded by

Explanation

The addition of HCN to compounds preceeds as follows:
`R-underset(delta^(+))overset(O^(delta^(-)))overset(||)C-R+CN^(-)overset("Slow")hArrR-underset(CN)underset(|)overset(O^(-))overset(|)C-Runderset("Fast")overset(H^+)rarrR-underset(CN)underset(|)overset(OH)overset(|)C-R`
In base, `CN^(-)` is formed from HCN while in acidic medium, the ionization of HCN to give `CN^(-)` is suppressed.