Which pair of elements has the most similar properties? (a) Sr and Ba (b) S and Ar(c) H and He (d) K and Se
The Correct Answer and Explanation is:
The correct answer is: (a) Sr and Ba
Explanation:
Elements with the most similar properties are those found in the same group (column) of the periodic table because they have the same number of valence electrons, which determines their chemical behavior.
Strontium (Sr) and Barium (Ba) are both in Group 2, known as the alkaline earth metals. This group includes elements like Be, Mg, Ca, Sr, Ba, and Ra. They each have two valence electrons, which makes them highly reactive metals that readily lose those two electrons to form +2 cations. Because of their similar electron configurations and position in the periodic table, Sr and Ba exhibit nearly identical chemical properties such as:
- Forming ionic compounds with halides (like SrCl₂ and BaCl₂)
- Reacting with water to form hydroxides and hydrogen gas
- Having similar reactivity trends (reactivity increases down the group)
- Forming basic oxides
Now let’s briefly look at why the other options are incorrect:
(b) S and Ar:
Sulfur is a reactive nonmetal in Group 16, while Argon is a noble gas in Group 18. Argon is chemically inert due to its complete outer shell, whereas sulfur is quite reactive and commonly forms -2 anions. Their properties are very different.
(c) H and He:
Hydrogen is a reactive nonmetal and often behaves like an alkali metal or a halogen in bonding. Helium is a noble gas and extremely unreactive. Despite being adjacent on the table, they are chemically dissimilar.
(d) K and Se:
Potassium is an alkali metal (Group 1) and very reactive. Selenium is a nonmetal in Group 16. Their properties differ significantly.
Thus, the pair with the most similar chemical properties is Sr and Ba, due to their shared group and common metallic behavior.
