A rifle barrel has a spiral groove which imparts spin to the bullet. Why?

Look at leaves of the same plant on the shady side and compare it with the leaves on the sunny side. Or, compare the potted plants kept in the sunlight with those in the shade. Which of them has leaves that are darker green? Why?

There is a tennis ball and a cricket ball of equal volume. Which one has greater inertia and why?

Amongst LiF and LiI which has more covalent character and why?

A company sells biscuitws. For packing purpose they are using cuboidal boxes : box A rarr 3 cm xx 8 cm xx 20 cm, box B rarr 4 cm xx 12 cm xx 10 cm . What size of the box will be econmical for the company? Why? Can you suggest any other size (dimensions) which has the sdame volumne but is more economical than these?

Which transition metal of 3d series has positive E^@ (M^(2+)//M) value and why ?

Which one of the following has the highest dipole moment and why: CH_2Cl_2 , CHCl_3 , C Cl_4