I think it's D, because theoretical yield is like, the yield you'd get if 100% of the reactants formed to make product. Well that's how I think of it, but it has something to do with limiting reagents and stuff. Sorry this isn't a really detailed explanation.
Lbs
a person is likely to weigh a few pounds
K₂SO₄ + CaI₂ → CaSO₄ + KI
K: 2 K: 1
S: 1 S: 1
O: 4 O: 4
Ca: 1 Ca: 1
I: 2 I: 1
↓
K₂SO₄ + CaI₂ → CaSO₄ + 2KI
K: 2 K: 2
S: 1 S: 1
O: 4 O: 4
Ca: 1 Ca: 1
I: 2 I: 2