Using Markovnikov's rule, correctly predict the principal product of the following reactions:
(i) `"But-1-ene"+HIrarr`
(ii) `"Vinyl chloride"+HIrarr`
(iii) `But-2-"ene"+HIrarr`
(iv) `2-"Methylbut-2-ene"+HIrarr`
(v) `"Pent-2-ene"+HIrarr`
Strategy: Use Markovnikov's rule for unsymmetrical alkenes: Positive part of the addendum ( adding molecule, `HI`) gets attached to that doubly bonded carbon atom which possesses more number of hydrogen atoms:

Explanation

(i)
Since `but-2-2"ene"` is a symmetrical alkene, Markovnikov's ruel is of no use. The reaction leads to the formation of just one product.

In `"Pent-2-ene"`, each of the doubly bonded carbons holds one hydrogen. Thus, neither product should predominate in accordance with the rule. Roughly, equal amounts of the two isomers are obtained.