= Solution
For $|\psi\rangle=a|0\rangle+b|1\rangle$, the <Controlled-NOT gate> gives
$$
CX(|\psi\rangle|0\rangle)=a|00\rangle+b|11\rangle.
$$
A cloned product would instead be
$$
|\psi\rangle|\psi\rangle
=a^2|00\rangle+ab|01\rangle+ab|10\rangle+b^2|11\rangle.
$$
Equality up to a physically irrelevant global phase requires $ab=0$. Thus
$$
\boxed{CX\text{ clones precisely the computational-basis states }|0\rangle\text{ and }|1\rangle,\text{ up to phase}.}
$$
For a genuine superposition it creates <quantum entanglement> instead of two independent copies.
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