1. Convert kilograms to grams:

* 1.0 kg = 1000 g

2. Calculate the number of moles:

* Molar mass of H₂ = 2 g/mol (1 g/mol for each hydrogen atom)

* Moles of H₂ = mass / molar mass = 1000 g / 2 g/mol = 500 mol

3. Use Avogadro's number:

* Avogadro's number = 6.022 x 10²³ molecules/mol

* Number of molecules = moles x Avogadro's number

* Number of molecules = 500 mol x 6.022 x 10²³ molecules/mol

* Number of molecules = 3.011 x 10²⁶ molecules

Therefore, there are approximately 3.011 x 10²⁶ hydrogen molecules in 1.0 kg of hydrogen gas.