Which of the reactants in this reaction is the limiting reagent? which is the reagent in excess?
sodium bicarbonate (s) + hydrochloric acid (aq) -> sodium chloride (aq) + carbon dioxide (g) + water:
nahco3 (s) + hcl (aq) -> nacl (aq) + co2 (g) + h2o (l)

the option 4) 2.0 mL of 10.5 M H₂O₂, where H₂O₂ has a molar mass of 34 g/mol.

Its concentration is 10.5 M.

Explanation:

1) The unit M means molar. It is the molarity of the solution.

Molartity is the concentration of the solution expressed as number of moles of solute per liters of solution.

The formula of molarity, M, is:

M = number of moles of solute / volume of solution in liters

2) 2.0 mL of 10 M H₂SO₄, where H₂SO₄ has a molar mass of 98 g/mol

⇒ concentration is 10 M

3) 5.0 mL of 1.0 M PbSO₄, where PbSO₄ has a molar mass of 303 g/mol

⇒ concentration = 1.0 M

4) 2.0 mL of 10.5 M H₂O₂, where H₂O₂ has a molar mass of 34 g/mol

⇒ concentration is 10.5 M

5) 100 mL of 10 M NaCl, where NaCl has a molar mass of 58 g/mol

⇒ concentration is 10 M