Can anybody tells me how many times a webhost server is expected to be down in a year.
I am practically running nuts right now.

Regardless of claims by web hosting companies about guaranteed server uptime the fact remains that the number of websites on any given server has a huge role to play on the reliability of the server itself because these websites will come with their unique visitors and all the work will be expected to be done or processed by the machine and this is where the processors of the machines come in, the higher the better.

A single server could host just 1, 500, or 5,000 websites so it is left for you to know which configuration will be more reliable than the rest.

All web servers should be configured to discourage downtime if possible all the time.

I have a dedicated server and I take time to fine tune the settings from the PHP to the MySQL database to ensure that things go well and that is assuming that the quality of the codes (especially for database driven websites) is ok because bad codes may hang or even crash a server.