I disagree,
During condensation, the -OH is removed from the carboxyl group and the -H is removed from the amino group - so it would be C-N covalent linkage.
Number 4 is true.
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As for number 3,
Proteins are positive at pHs below their Isoelectric points (pI) due to higher protonation. Therefore, this proteins pI is higher than pH7. Lowering the pH will increase the concentration of protons and can therefore only protonate more residues on the protein (make it more positive).
So the net positive charge WOULD NOT decrease.