Who invented vaccination for small pox?

The number of isotopes in the hydrogen is:

Acid rain is caused due to pollution of atmosphere by 

The release of which of the following into ponds and wells helps in controlling mosquitoes?

Who is thought to have invented the thermo scope?

Which of the following metals occurs in Free State?

As compared to pure water, a body in salty water will :

What would remain unchanged if a sound travels from air to water ?