jmc

Since the number is even, the last digit must be $2$ or $4$. To make the smallest possible number, the ten-thousands digit must be as small as possible, so the ten-thousands digit is $1$. Simillarly, the thousands digit has second priority, so it must also be as small as possible once the ten-thousands digit is decided, so the thousands digit is $2$. Similarly, the hundreds digit needs to be the next smallest number, so it is $3$. However, for the tens digit, we can't use $4$, since we already used $2$ and the number must be even, so the units digit must be $4$ and the tens digit is $9,\boxed{9}$ (The number is $12394$.)