How many valence electrons does a copper atom have? The valence electron configuration of $\ce{Cu}$ is $\ce{4s^1 3d^{10}}$. According to this the answer is $11$, but shouldn't it be $1$ since the d shell is already filled up?
Yes, copper only has 1 valence electron. Remember: valence electrons only include the electrons in the highest energy (n) shell.