Explain why:

i.                    Alkali metals are good conductors of electricity.

ii.                  Lithium has the highest ionization energy in the group.

iii.                Sodium forms +1 ion and not +2 ion.

iv. Group 1 elements form ionic compounds.

Answer:

Explain why:

i.                    Alkali metals are good conductors of electricity.

Alkali metals are good conductors of electricity. They have one electron in their outermost shell that is held/retained very weakly by the nucleus.  The outer electron can move freely and drift further away from the nucleus. Large amounts of free-flowing electrons in the outer shells conduct electricity through the metal when an electric field is applied.

ii. Lithium has the highest ionization energy in the group.

 Lithium has the highest ionization energy in its group. It is due to the high hydration energy of small lithium-ion which more than compensates for high ionization enthalpy. Li-ion has a very high hydration energy, and as a result, its reduction potential is quite low (E°= -3). In an aqueous solution, lithium is the most effective reducing agent.

iii. Sodium forms +1 ion and not +2 ion.

Sodium forms Na⁺ ion but it does not form Na²⁺ because of the low value of (IE)1? and high value of (IE)2?.

Sodium has one valence electron. Sodium forms Na+ ion by losing its valence electron and attains the stable electronic configuration of Ne with a completed octet. This requires less energy. The removal of the second electron will break this stable electronic configuration and requires high energy.

iv. Group 1 elements form ionic compounds.

Group one elements will form ionic compounds with nonmetallic elements from the main group elements of groups 12-17. This can be explained by the large electronegativity differences between the alkali metals and the nonmetal elements. Electronegativity measures the relative "pull" an element has on electrons in a bonding situation. Relatively equal values, as between nonmetal elements, leads to the formation of a bond by sharing electrons between the atoms, i.e. covalent bonding. If the difference is large enough, the more electronegative element essentially captures the electron leading to the formation of anions and cations and ionic bond formation.
The explanation of why the electronegativities differ between metals and nonmetals comes down to nuclear charge effects. As one builds up atoms moving across a period, keep in mind that one proton is added to the nucleus for every electron added to the outermost electron shell. It is the stronger nuclear attraction experienced by an electron filling the last few vacancies of the nonmetals' outer shell as opposed to that experienced by the few outer shell electrons of the metal atoms that leads to electron transfer.

References:

http://www.passmyexams.co.uk/GCSE/chemistry/physical-properties-of-alkali-metals.html

https://www.zigya.com/study/book?class=11&board=mbose&subject=Chemistry&book=Chemistry+Part+II&chapter=The+s-Block+Elements&q_type=&q_topic=Anomalous+Properties+of+Lithium&q_category=&question_id=CHEN11092654

https://www.toppr.com/ask/question/sodium-forms-na-ion-but-it-does-not-form-na2-because-of-the/

https://www.quora.com/Why-do-the-group-1-elements-form-ionic-compounds