The correct option is B Mn
According to Berzelius system, while writing a chemical symbol:
∙ The first letter is always capital and second one is always small.
∙ If the first two letters of the elements are the same, then the next prominent letter should be used.
∙ Magnesium and manganese both have 'Ma' in their names. Hence, the next letter is selected for their atomic symbols.
Therefore, the symbol of magnesium is Mg and that of manganese is Mn.