Question

which of the following decreases with increasing atomic number in group 2a?
number of electrons
ionization energy
shielding effect
ionic size

Explanation:

• Number of electrons: In Group 2A, as atomic number increases, the number of electrons increases (since atomic number = number of protons = number of electrons in a neutral atom).
• Ionization energy: Ionization energy is the energy required to remove an electron. In Group 2A, as we move down the group (increasing atomic number), the atomic radius increases. The outermost electrons are further from the nucleus and are more shielded. So, less energy is required to remove an electron, and ionization energy decreases.
• Shielding effect: As atomic number increases in Group 2A, there are more electron - filled inner shells. So, the shielding effect (the reduction of the effective nuclear charge on the outer - shell electrons due to the presence of inner - shell electrons) increases.
• Ionic size: For Group 2A elements, when they form ions (by losing 2 electrons), as atomic number increases, the ionic radius increases. This is because there are more electron shells in the ions of heavier elements in the group.

Answer:

ionization energy