could u pls suggest me some topic for my bio investigatory project so that i could prepare a good project file on it

You can go for some investigatory projects which aims at finding the amounts of a compound in different food items like

• Estimation of nicotine in different brands of cigarette
• Estimation of caffeine in different brands of drinks like tea, coffee etc.
• Estimation of calcium, fluorine etc. in different brand of toothpaste.
• Estimation of acid content in different fruits and vegetable juices etc.

You can also consider the ones mentioned by your friend. Try finding some more on your own.