Solve the Equation: Finding the Missing Number in 800-?=800

To solve this problem, we must determine which number, when subtracted from 800, results in 800. We can solve this by recognizing certain properties of numbers.

• Step 1: Identify the equation $800 - ? = 800$.
• Step 2: Understand that for the equation to hold, the value of '?' must be such that subtracting it leaves 800 unchanged.
• Step 3: Recognize that zero has the property $x - 0 = x$ for any number $x$.

So, substituting zero for '?', we have:
$800 - 0 = 800$, which is true.

Therefore, the number that satisfies the equation $800 - ? = 800$ is $0$. The correct choice is therefore option 2.