Pb(OH)2:
Molar mass of Pb = 207.2 g/mol
Molar mass of O = 16.00 g/mol
Molar mass of H = 1.008 g/mol

Molar mass of Pb(OH)2 = 207.2 + 2(16.00 + 1.008) = 207.2 + 34.016 = 241.216 g/mol

Sr(OH)3:
Molar mass of Sr = 87.62 g/mol

Molar mass of Sr(OH)3 = 87.62 + 3(16.00 + 1.008) = 87.62 + 51.048 = 138.668 g/mol

Co(OH)3:
Molar mass of Co = 58.93 g/mol

Molar mass of Co(OH)3 = 58.93 + 3(16.00 + 1.008) = 58.93 + 51.048 = 109.978 g/mol

Ba(OH)2:
Molar mass of Ba = 137.33 g/mol

Molar mass of Ba(OH)2 = 137.33 + 2(16.00 + 1.008) = 137.33 + 34.016 = 171.346 g/mol

RbOH:
Molar mass of Rb = 85.47 g/mol

Molar mass of RbOH = 85.47 + 16.00 + 1.008 = 85.47 + 17.008 = 102.478 g/mol

Therefore, the molar masses are:
Pb(OH)2 = 241.216 g/mol
Sr(OH)3 = 138.668 g/mol
Co(OH)3 = 109.978 g/mol
Ba(OH)2 = 171.346 g/mol
RbOH = 102.478 g/mol