Here's how to calculate the number of molecules in 13.77 lb of magnesium bromide (MgBr₂):

1. Convert pounds to grams:

* 1 lb = 453.592 grams

* 13.77 lb * 453.592 g/lb = 6250.83 g

2. Calculate the molar mass of magnesium bromide:

* Mg: 24.305 g/mol

* Br: 79.904 g/mol

* MgBr₂: 24.305 + (2 * 79.904) = 184.113 g/mol

3. Calculate the number of moles:

* Moles = Mass / Molar Mass

* Moles = 6250.83 g / 184.113 g/mol = 34.00 mol

4. Calculate the number of molecules:

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

* Molecules = Moles * Avogadro's number

* Molecules = 34.00 mol * 6.022 x 10²³ molecules/mol = 2.05 x 10²⁵ molecules

Therefore, there are approximately 2.05 x 10²⁵ molecules of magnesium bromide in 13.77 lb.