I uh need help with stoichiometry like pretty pls thank u :,))

The answer to your question is below

Explanation:

21.-

mass of Cr = ?

mass of Cu = 27 g

balanced chemical reaction

                2Cu  +  3CuSO₄   ⇒    Cr₂(SO₄)₃  + 3 Cu

-Look for the molar mass of Copper and chromium

Cr = 52 g

Cu = 63.6 g            

                      52 g of Cr 63.5 g of Cu

                        x               27 g of Cu

                              x = (27 x 52) / 63.5 g

                             x = 22.1 g of Cr

22.-

Theoretical yield of NO₂ = ?

mass of Pb(NO₃)₂

Balanced chemical reaction

                2Pb(NO₃)₂   ⇒   2PbO  +  4NO₂  +  O₂

Process

-Calculate the molar mass of Pb(NO₃)₂ and NO₂

Pb(NO₃)₂ = 2 [ 207 + (14 x 2) + (16 x 6)]

               = 2[207 + 28 + 96]

               = 662 g

NO₂ = 4[ 14 + (16 x 2)]

       = 4[14 + 32]

       = 184 g

- Calculate the theoretical yield

                  662 g pf Pb(NO₃)₂ 184 g of NO₂  

                    9.95 g of Pb(NO₃)₂     x

                              x = (9.95 x 184) / 662

                             x = 2.76 g of NO₂

-Percent yield

 Percent yield = actual yield / theoretical yield x 100

                        = 2.12/2.76 x 100

                       = 76.8 %

23.-

balanced chemical reaction

                2SO₂  +  O₂  +  2H₂O  ⇒   2H₂SO₄

mass of O₂ = ?

mass of H₂SO₄ = 56.1 g  

-calculate the molar mass of O₂ and H₂SO₄

O₂ = 32 g

H₂SO₄ = 2[2 + 32 + 64] = 196 g

                    32 g of O₂  196 g of H₂SO₄

                      x                56.1 g of H₂SO₄

                             x = (56.1 x 32) / 196

                             x = 1795.2 / 196

                            x = 9.2 g of O₂

the answers would be

the first one and the second one