You're going to divide the mass of chlorine within the compound by the mass of the compound, and then multiply the result by 100 to get the answer
Answer : Option A) Atomic number of Arsenic is 33.
Explanation : Arsenic contains same number of protons in its atomic nucleus. In arsenic there are 33 protons found in the atomic nucleus. Hence, the atomic number will be 33. It has 5 valence electrons in its outermost shell, which is also called as valence shell. So, its valency becomes 5.
potassium belongs to group IA of the periodic table.