I will unfortunately have to agree with RaBBiT here. The question says "Which is proper English", and "Egg yolks are white" is proper English.
If you want to switch it to "Which is correct", then you're doing good.
Also, for my socks question, you'd have to say "there are 20 socks of each color..." which is what you should also say with your Socks question. Extra facts help mislead people