Molar mass CuSO4.5H2O => 249.685 g/mol
Volume in liters => 100 mL / 1000 => 0.1 L
1 L ----------------- 0.05 M
0.1 L -------------- ?? ( moles of copper sulfate pentahydrate )
0.1 x 0.05 / 1 => 0.005 moles
1 mole ------------- 249.685 g
0.005 moles ------- ( mass of copper sulfate pentahydrate )
0.005 x 249.685 / 1 => 1.28425 g CuSO4.5H2O
hope this helps!