Conversation so far:
What is the lowest rank in the Hereditary peerage?
The ranks of the Peerage in most of the United Kingdom are, in descending order of rank, Duke, Marquess, Earl, Viscount and Baron.
How does one address a baron in the Hereditary peerage?
What is the next higher rank after baron in the Hereditary peerage?
After the rank of Baron is Viscount.

Question: How many Viscounts are there?
Self-contained rewrite: How many Viscounts are there in the Hereditary peerage?