Name the alkene with molecular formula $C_{10}H_{20}$.

Reaction of ethanol with conc. sulphuric acid at $170^{\circ} C$ produces a gas which is then treated with bromine in carbon tetrachloride. The major product obtained in this reaction is

Which of the following does not follow $M.K.$ (Markownikoff's) rule?

Assertion $(A)$: Reaction of $but-1-ene$ with $HBr$ gives $1-bromobutane$ as the major product.
Reason $(R)$: Addition of $HBr$ to unsymmetrical alkenes proceeds according to Markovnikov's rule.
The correct answer is

$A$ gas decolourises Bayer's reagent but does not react with Tollen's reagent. This gas is:

In which case does the addition of an electrophile $NOT$ take place according to Markovnikov's rule?