Smoke screen is used in warfare for the purpose of concealment and camouflage. Smoke screens generally consists of fine particles of –

Which of the following is used in fire alarm?

Which one of the following metals is most commonly used for making filament of incandescent electric bulbs?

Which one of the following is used in soda-acid fire extinguishers?

Which compound is used for increase of octane rating?

Which one of the following sodium compounds is used for softening hard water ?