Answer:
Respond "1"$1$.
Explanation:
Put x into binary - the. The number of 1s in the result is the answer. $$\begin{align}5&=101 \rightarrow 2 \\ 6&=110 \rightarrow 2 \\ 3&=11 \rightarrow 2 \\ 2&=10 \rightarrow 1 \\ 0&=0 \rightarrow 0 \\ 4&=100 \rightarrow 1\end{align}$$Here is a key for the given numbers: $$\begin{align}5&=101 &\rightarrow 2 \\ 6&=110 &\rightarrow 2 \\ 3&=11 &\rightarrow 2 \\ 2&=10 &\rightarrow 1 \\ 0&=0 &\rightarrow 0 \\ 4&=100 &\rightarrow 1\end{align}$$