The soldiers of Napolean army while at Alps during freezing winter suffered a serious problem as regards to the tin buttons of their uniforms. White metallic tin buttons got converted to grey powder. This transformation is related to

Question

( A ) a change in the partial pressure of oxygen in the air
( B ) an interaction with water vapour contained in the humid air
( C ) an interaction with nitrogen of the air at very low temperatures
( D ) a change in the crystalline structure of tin