What are the defined differences and duties between an Viscount and a Viceroy?

A Viscount is a peer who ranks above a Baron and below an earl (or, in Europe, a count). Viscount is also used as a courtesy title for an earl's heir - for example, Princess Diana's brother was known as Viscount Althorp before he inherited the title Earl Spencer. A viscount has no defined duties as such, for the title is hereditary.
https://en.wikipedia.org/wiki/Viscount
A Viceroy, however, is a royal appointment and is more or less a governor-general, who runs a colony, territory etc in the name of and as the representative of the monarch. In the days of British India, the viceroy was appointed by the reigning monarch and supervised the administration of the Raj and liaised with the rulers of the Princely States. He reported directly to the Secretary of State for India and had the British Indian Army at his disposal. Lord Louis Mountbatten was the last viceroy of India.
https://en.wikipedia.org/wiki/Viceroy