The mass of magnesium produced can be calculated using Faraday's laws of electrolysis.

According to Faraday's first law, the amount of a substance deposited or liberated at an electrode during electrolysis is directly proportional to the quantity of electricity passed.

The molar mass of magnesium (Mg) is approximately 24.3 g/mol.

The charge of one mole of electrons (1 Faraday) is approximately 96485 Coulombs. 

Given that the cell is operating at 500 Amperes for 24 hours, the total charge passed (Q) can be calculated as follows:

Q = It = 500 A * 24 hours * 3600 seconds/hour = 43200000 Coulombs

The number of moles of magnesium produced (n) can be calculated using the charge passed and the charge of one mole of electrons:

n = Q / (2 * Faraday) = 43200000 C / (2 * 96485 C/mol) = 223.6 mol

The factor of 2 in the denominator is because magnesium ion (Mg2+) requires two moles of electrons to be reduced to magnesium metal.

Finally, the mass of magnesium produced (m) can be calculated using the number of moles and the molar mass:

m = n * Molar mass = 223.6 mol * 24.3 g/mol = 5435.48 g = 5.435 kg