Question

Choose the incorrect formula out of the four compounds for an element X below:
  (A) ${{X}_{2}}{{O}_{3}}$
  (B) ${{X}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$
  (C) $XP{{O}_{4}}$
  (D) ${{X}_{2}}C{{l}_{3}}$

Answer 1

Hint: From the given formulas we can find the oxidation state of X in molecular formula. Among the given options A is an oxide, B is sulphate, C is phosphate and D is a chloride molecule. By knowing the oxidation states of these common ions we could verify each of the molecular formulas.

Complete answer:
- Let’s start with the concepts of molecular formulas. They describe the exact type and number of atoms in a single molecule of a compound. The number of atoms of each element present in each molecule is shown as a subscript following that element’s symbol and the component elements are usually represented by their chemical symbols.
-The molecular formula gives us information about the charge of the atoms in molecules, about the proportions of atoms which constitutes a specific chemical compound, etc. We are given an element X and we don’t have an idea about its oxidation state.
- As we know oxygen generally has a −2 charge and from the molecular formula ${{X}_{2}}{{O}_{3}}$ we can find that X has a +3 oxidation state. The chargers are getting balanced and thus option (A) is the correct formula.
- In option (B) sulfate is present which has the oxidation state of −2 since sulphate is $S{{O}_{4}}^{^{2-}}$. Here in ${{X}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$ X is thus having a +3 oxidation state since the chargers are getting balanced and thus option (B) is correct formula.
- In option (C) phosphate is present which has the oxidation state of −3 since phosphate is $P{{O}_{4}}^{^{3-}}$ .In ${{X}_{2}}{{\left( S{{O}_{4}} \right)}_{3}}$ also X is having a +3 oxidation state and the chargers are getting balanced and thus option (C) is also a correct formula.
- From the above options it’s clear that X has a +3 oxidation state. Consider${{X}_{2}}C{{l}_{3}}$. As we know chlorine has −1 oxidation state. Since there are three chlorine atoms they overall provide a −3 oxidation state thus balancing the +3 oxidation state of X. Thus the molecular formula will be $XC{{l}_{3}}$. Therefore the formula ${{X}_{2}}C{{l}_{3}}$ is incorrect.

Therefore the answer is option (D). ${{X}_{2}}C{{l}_{3}}$ .

Note:
Keep in mind that there are three major sorts of chemical formulas such as empirical, molecular and structural formulas. The structural formulas show how the atoms in a molecule are bonded to each other, the empirical formula shows the simplest whole-number ratio of atoms in a compound and molecular formulas show the number of each type of atom in a molecule.