Statement I: Lithium needs less energy to knock off an electron from its outermost orbit than Helium.
Statement II: Lithium has 1 electron in its outermost orbit which is loosely bonded to the nucleus, due to the repulsion of the electrons present in the inner orbit and located at a greater distance from the nucleus.
Statement I is true. Statement II is true. Statement II is the correct explanation of statement I.
In Lithium, there are 2 electrons in the first orbit and the remaining one electron is in the second orbit. This electron experiences less attraction from the nucleus due to the increased distance from the orbit. Also, the electrons in the first orbit repel the 3rd electron which further reduces the net force on the outermost electron.
Hence, it is easy to knock off the outermost electron in Lithium when compared to Helium.