What is the smallest five-digit number, whose digits are all different?

12345

Step-by-step explanation:

1,) select lowest whole number for ten-thousandth place

2.) not using numbers already used. select the next lowest whole number for thousands. place

3 ...) select the next lowest number for hundredths place

4.) select the next lowest whole number for tenths place

5.) select the next lowest whole number for the singles place