Which of the following pairs of properties of alkali metals decreases down the group?
Answer Details
The pair of properties of alkali metals that decreases down the group is "first ionization energy and melting point".
First ionization energy refers to the energy required to remove an electron from an atom. As we move down the group in the periodic table, the number of occupied energy levels increases, resulting in an increase in the distance between the nucleus and the outermost electron. This means that the force of attraction between the nucleus and the outermost electron decreases, making it easier to remove the electron. Hence, the first ionization energy decreases down the group.
Melting point refers to the temperature at which a solid substance changes into a liquid state. As we move down the group, the size of the atoms increases due to the addition of new electron shells. This results in weaker metallic bonding between the atoms, which requires less energy to overcome, leading to a decrease in melting point down the group.
Therefore, the correct pair of properties that decrease down the group for alkali metals is "first ionization energy and melting point".