An element A (atomic weight = 12) and B (atomic weight = 35.5) combines to form a compound X. If 4 mol of B combines with 1 mol of A to give 1 mol of X. The weight of 1 mol of X would be:
(A) 47.5 g
(B) 74.0 g
(C)154.0 g
(D) 148.8 g

Hint: For this problem, firstly we have to write the complete reaction of the formation of the compound X. After which we can apply the formula of calculating the molecular mass of the compound.

Complete step by step solution:
-In the given question, we have to calculate the weight of 1 mol of the compound which is formed by the reaction between A and B.
-As we know that molecular weight is the net sum of all the atomic weight which also means that with an increase in the molecular weight the density of the molecule also increases.
-Now, it is given in the question that the atomic weight of an element A and B are 35.5 and 12 respectively.
-Also, we know that the 4 mole of B combines with 1 mol of A to yield 1 mol of X.
-So, the balanced chemical reaction will be:
$\text{4B + A }\to \text{ A}{{\text{B}}_{4}}$
-Now, as we know that to calculate the molecular weight we have to add the atomic weight of each element along with it we have to multiply the weight with the number of moles of the respective element.
-So, the weight of 1 mole of X will be:
$1\text{ }\times \text{ 12 + }\text{4 }\times \text{ 35}\text{.5 = 154g}$
-So, the weight of 1 mole of X whose molecular formula is $\text{A}{{\text{B}}_{4}}$ is 154.0 grams.

Therefore, option (C) is the correct answer.

Note: A mole of any substance or a particle is equal to the Avogadro's number which is equal to $\text{6}\text{.022 }\times \text{ 1}{{\text{0}}^{23}}$ particles such as electrons, proton, atom, etc. The mole is very important for calculating the large quantities.