X is an element with Atomic number = 20. What will be the formula of its chloride?
The atomic number 20 indicates that the electronic configuration of element is 2,8,8,2. The number of electrons in valence shell is 2. Thus its valency is 2. So the formula of its chloride will be MCl2. Moreover we know that calcium has an atomic number=20, therefore the exact molecular formula will be CaCl2.