Question

Ethene reacts with Y to produce ethanol.
Ethene$ + $ Y$ = $ Ethanol
What is Y?
A: Hydrogen
B: Oxygen
C: Steam
D: Yeast

Answer 1

Hint: Chemical formula of ethene is ${C_2}{H_4}$ . It is commonly known as ethylene. It comes under the category of alkenes which are unsaturated hydrocarbons. Unsaturated hydrocarbons are those which have double or triple bonds between carbon-carbons. Chemical formula of ethanol is ${C_2}{H_6}O$ . It comes under the category of alcohol.

Complete step by step solution:
When we observe given molecules closely we find that if somehow we add water molecules in ethene we will get ethanol. Reaction in which a substance combines with water is called hydration reaction. Conversion of ethene to ethanol is an example of hydration reaction. In this reaction ethene is heated with steam in the presence of phosphoric acid (which is a catalyst used to speed up the reaction).
${C_2}{H_4} + {H_2}O\xrightarrow[{}]{{}}{C_2}{H_5}OH$
So, the answer to this question is option C i.e. steam.

Additional information: Dehydration reactions are opposite to hydration reactions. These are the reactions in which there is removal of water molecules from the reactant. Dehydrating agents are the agents that help in removal of water. Common used dehydrating agents are sulphuric acid and alumina.
Hydrogenation reactions are the reactions in which hydrogen molecules are added in the reactants. This reaction is widely used to convert unsaturated hydrocarbons (those which have double or triple bonds between carbon-carbon) to saturated hydrocarbons (those having single bonds between carbon-carbon).
Halogenation reactions are those in which one or more halogens are added to reactant species. Halogens are a group of $17$ members of periodic table. Examples of halogens are chlorine, bromine, iodine, fluorine etc.

Note: To solve such reactions of organic chemistry identify difference between atoms of reactants and products. Like in this example there was a difference of water molecule. You can simply use the elimination method after identifying this. Like there was only one option which could be the possible way to add water molecules.