Read the given passage and answer the questions The substitution reaction of alkyl halide mainly occurs by S_(N)1 or S_(N)2 mechanism. Whatever mechanism alkyl halides follow for the substitution reactionto occur, the polarity of the carbon hallogen bond is responsible for these substitution reactions. The rates of S_(N)1 reactions are governed by the stability of carbocation whereas for S_(N)2 reactions steric factor is the deciding factor. If the starting material is a chiral compound, we may end up with an inverted product or racemic mixture depending upon the type of mechanism followed by alkyl halide. Cleavage of ethers with HI is also governed by steric factor and stability of carbocation, which indicates that in organic chemistry, these two major factors help us in deciding the kind of product formed. Q. Name the instrument used for measuring the angle by which the plane, polarised light is rotated.