Arrange the elements of the second period in increasing order of their electron affinity. Name the elements which do not follow the trend in this period.

The second period of the periodic table includes the elements lithium (Li), beryllium (Be), boron (B), carbon (C), nitrogen (N), oxygen (O), fluorine (F), and neon (Ne). Electron affinity refers to the energy released or absorbed when an atom gains an electron to form a negatively charged ion.

The electron affinity generally increases from left to right across a period. However, there are some exceptions in the second period. Here's the arrangement of the elements in increasing order of their electron affinity:

Neon (Ne) - Neon has the highest electron affinity in the second period.
Helium (He) - Although not part of the second period, it comes before lithium (Li) in the periodic table and has the second-highest electron affinity.
Argon (Ar) - Again, not part of the second period, but it comes after neon (Ne) and has the third-highest electron affinity.
Fluorine (F) - Fluorine comes next in terms of electron affinity, although it is not higher than helium (He) or argon (Ar).
Oxygen (O) - Oxygen follows fluorine with a lower electron affinity.
Nitrogen (N) - Nitrogen has a lower electron affinity than oxygen.
Carbon (C) - Carbon comes next with a lower electron affinity.
Beryllium (Be) - Beryllium has the second-lowest electron affinity in the second period.
Lithium (Li) - Lithium has the lowest electron affinity in the second period.
The two elements that do not follow the trend in this period are helium (He) and neon (Ne), which have higher electron affinities than lithium (Li) and beryllium (Be). This deviation can be attributed to their stable electron configurations due to completely filled s-subshells (for helium) and completely filled s and p subshells (for neon).