Question

which of the following will have a lower ionization energy than scandium (sc)? calcium (ca), titanium (ti), helium (he), magnesium (mg)

Explanation:

Step1: Recall ionization - energy trends

Ionization energy generally increases across a period and decreases down a group in the periodic table. Scandium (Sc) is in the fourth - period and group 3.

Step2: Analyze each element

• Calcium (Ca) is in group 2 and the fourth period. It has a lower effective nuclear charge than Sc in the same period, so its first - ionization energy is lower.
• Titanium (Ti) is in group 4 and the fourth period. It has a higher effective nuclear charge than Sc, so its ionization energy is higher.
• Helium (He) is a noble gas in the first period. Noble gases have very high ionization energies due to their stable electron configurations.
• Magnesium (Mg) is in group 2 and the third period. Although it has a stable electron configuration in its outer shell, it is in a lower period than Sc, and its first - ionization energy is not lower than Sc's considering the general trends.

Answer:

Calcium (Ca)