[poll id=”70″]
ANSWER: A. 23 g/mol
Looking at the periodic table, add up the molar mass of the elements that are known. 2 K gives (39+39), and 2F gives (19+19):
39+39+19+19=116
Thus, 116 is 46 short of the total 162, thus there has to be 46 g of the unknown ‘X’. Since there are 2 moles of this, the atomic weight of this element has to be 23 g/mol.