What is the theoretical yield in liters of hydrogen at stp if 20.1g of calcium are completely reacted

Calcium reacts with water to produce Calcium Hydroxide and Hydrogen gas;

                            Ca  +  2 H₂O    →    Ca(OH)₂  +  H₂

According to balance equation,

                 40 g (1 mole) Ca reacts to form  =  22.4 L (1 mole) H₂
So,
                           20.1 g of Ca will produce  =  X L of H₂

Solving for X,,
                                        X  =  (22.4 L × 20.1 g) ÷ 40 g

                                        X  =  11.25 L

Result:
          Theoretical Yield of H₂ at STP  =  11.25 Liter