Which statement(s) regarding the trends in Period 3 elements of the periodic table is/are correct?

1. The first ionisation energy of aluminium is lower than that of magnesium because the outer electron in aluminium is in a $3p$ orbital, which is higher in energy than the 3s orbital and shielded by the 3s² electrons.
2. Electronegativity increases from sodium to chlorine because the nuclear charge increases while shielding remains approximately constant.
3. Phosphorus ($P_4$) has a higher melting point than sulfur ($S_8$) because phosphorus molecules are smaller and can pack more closely together, forming stronger covalent bonds.