Final answer:
The false statement is that an atom of argon will have a higher electron affinity than chlorine. Chlorine has a much higher electron affinity due to its tendency to complete its valence shell, whereas argon is a noble gas with a low affinity for extra electrons.
Step-by-step explanation:
The false statement among the ones provided is that an atom of argon will have a higher electron affinity than Cl (chlorine). Argon is a noble gas with a complete electron shell, so it has very low electron affinity as it does not tend to gain electrons. On the other hand, chlorine has a much higher electron affinity since it tends to gain an electron to complete its valence shell.
The correct answers for the other statements are:
1) an atom of strontium will indeed be larger than an atom of tellurium, due to its position further down the periodic table which indicates it has more electron shells;
2) a sulfide ion will be larger than a sulfur atom because it gains two electrons and the increased electron-electron repulsion causes the electron cloud to expand;
3) the third ionization energy of Mg will be much larger than the third ionization energy of Al because removing a third electron from magnesium involves taking an electron from a fully filled 2p orbital, while for aluminum it is taking an electron from a partially filled 3p orbital, which requires less energy due to less electrostatic attraction and greater shielding.