Elements P has an atomic number of 12 while element Q has an atomic number

Explanation

Element P has an atomic number of 12 while element Q has an atomic number of 15. The atomic number of an element is the number of protons in the nucleus of an atom of that element. The combination of P and Q gave a compound with the formula P m Q n . To determine the values of m and n, we need to use the valency of each element. The valency of an element is its combining power with other atoms. For example, an element with a valency of 2 can combine with two atoms of another element. Element P is in Group 2 of the periodic table, which means it has a valency of 2. Element Q is in Group 5, so it has a valency of 3. To form a neutral compound, the total positive charge of P and the total negative charge of Q must balance each other out. One way to achieve this is for two atoms of P to combine with three atoms of Q, giving the formula P 2 Q 3 . Therefore, the correct answer is option B: 2 and 3. It is important to understand the concept of valency in chemistry as it determines how elements react with each other to form compounds. For more information, please see the relevant sections of the recommended textbooks.