The answer for the 1st question
When kettle is heated we cannot touch the handle of the kettle because it also gets heated ,since it is made up of metal; which is a good conductor of heat. So  the handle of kettle is covered with cane so that we can touch the handle without getting burned . This is because cane is bad conductor of heat  
the answer 2nd question -

Definition of symbiotic relationship is -
Plants which live in association with other plant and share shelter and food ; such relationship is called Symbiosis ( living together ). Eg: Lichens, Nitrogen fixation by rhizobrium . 
Lichens- Lichens are composition of algae and fungus . Algae are microscopic plants and can be seen if there are many and have chlorophyll while fungi do not . Fungus helpsalga in absorption of water and nutrients and give shelter to it ; while alga prepares food which is shared by fungus. This is how the two organisms help each other. 
Nitrogen fixation by rhizobium -
A bacterium called rhizobium lives in the rootsof leguminous plantslike bean dal etc . This bacteria can fix nitrogen nitrogen gas from atmosphere and supply it to the plant in return the plant gives shelter and food to Rhizobium (as it cannot make its own food)
The answer of 4th question 
The answer of 5th question 
Mercury , i also 1st didn't believe but it is written on internet itself !!