Question

An element X that reacts with oxygen and forms an oxide ${X_2}O$. This oxide dissolves in water and turns red litmus blue. Element X is :
(A) Mg
(B) Cu
(C) Na
(D) Si

Answer 1

Hint: The metal X that will react with oxygen to give ${X_2}O$ product will be the one belonging to group 1 because such a type of product will be formed with the group I elements only that have one valence electron. The metal is an alkali metal that is soft in nature. The element has valence electrons in the 3s shell.

Complete step by step solution:
In such questions, let us start by writing what is given to us.
Given :
 X reacts with oxygen to form ${X_2}O$. This can be written as -
$X + {O_2} \to {X_2}O$
 ${X_2}O$ dissolves in water.
${X_2}O$turns red litmus blue. This means ${X_2}O$ is basic in nature because a base turns red litmus blue.

Now, let us see the options given to us one by one.
The first is Mg. The reaction of Magnesium with oxygen is as-
$Mg + {O_2} \to MgO$
The magnesium reacts with oxygen to give magnesium oxide and not ${X_2}O$ type product. So, this is not the right answer.
The second option is Cu. The copper reacts with oxygen to form-
$2Cu + {O_2} \to 2CuO$
The product here is copper oxide is of type XO and not ${X_2}O$. So, even this is not the correct answer.
The third option given to us is the sodium metal (Na). The reaction with oxygen is as -
$Na + {O_2} \to N{a_2}O$
The product with sodium is of the type ${X_2}O$. So, this is the correct answer.
The option (D) given to us is Silicon. The silicon is a non-metal that reacts with oxygen as -
$Si + {O_2} \to Si{O_2}$
The product formed when silicon reacts with oxygen is also not of the type ${X_2}O$.
So, the option (D) is also not the correct answer.

So, the correct answer is the option (C).

Note: It must be noted that the compounds formed by alkali metals can be mostly dissolved in water. The compounds of sodium and potassium show such characteristic behaviour. The sodium oxide dissolves in water and forms an alkali compound sodium hydroxide. The reaction for this is -
$N{a_2}O + {H_2}O \to 2NaOH$
This sodium hydroxide is basic in nature and turns red litmus blue.