Manganese dioxide oxidises hydrochloric acid to chlorine and gives manganous chloride and water.

Explanation

a) The skeleton equation is written as
`MnO_(2)+HClrarrMnCl_(2)+Cl_(2)+H_(2)O`
b) Focusing on the oxidation numbers
`overset(+4)(Mn)overset(-2)(O_(2))+overset(+1)(H)overset(-1)(Cl)rarr overset(+2)(Mn)overset(-1)(Cl_(2))+overset(0)(Cl_(2))+overset(+1)(H_(2))overset(-2)(O)`
c) Locating atoms undergoing change in oxidation numbers
`overset(+4)(Mn)O_(2)+Hoverset(-1)(Cl)rarroverset(+2)(Mn)Cl_(2)+overset(0)(Cl_(2))+H_(2)O`
d) Determining the change in oxidation numbers

e) Cris - crossing these changes in the oxidation numbers
`MnO_(2)+2HClrarrMnCl_(2)+Cl_(2)+H_(2)O`
f) Balancing the atoms other than hydrogen and oxygen
`MnO_(2)+2HCl+2HClrarr MnCl_(2)+Cl_(2)+H_(2)O`
g) Balancing the atoms hydrogen and oxygen
`MnO_(2)+4HClrarrMnCl_(2)+Cl_(2)+2H_(2)O`
This is the balanced equation.