In the diagram above, the time taken to trace a wave between P and Q is?

Which of the following materials does not serve as a safety device in electrical circuits? 
 

Which of the following liquids has the highest surface tension?
 

The nucleon and proton numbers of a neutral atom of an element are 238 and 92 respectively. Determine the number of neutrons in the atom. 

An instrument used to measure relative humidity is the?