How do government corporations differ from other corporations in the United
States?

Government corporations are intended to carry out business activities for the betterment of the citizens of the nations. These corporations are set up by the congress men and unlike all other public business they have board of directors and a general manager.

the answer is: must pay taxes on profits

since it is considered as a part of your income, profits from investments is eligible for tax payment.

the tax from your investment could be influenced by how long you decided to sell it. united states promotes keeping your investment for long term period. so, the tax rate for investments that you sell in less than one year is typically higher compared to investments that you sell in more than one year period.