Answer is: another name for groups of elements is family. There are 18 numbered groups in the periodic table. The elements in a group have similar physical or chemical characteristics and some groups have a specific name, for example group 17 (the halogens).
water is h2o, so the molar mass is 1.01x2+16.00=18.02. divide 4.5 x 10^22 by 6.022 x 10^23 to get 7.5 x 10^-2 (2 sig figs). 18.02 x 7.5 x 10^-2 is 1.35 g
