Answer :

lulu1991
The answer is (4) Rb. From observation, we can find that these four elements are from first column. The melting point from top to the bottom is from high to low. So the answer is (4).

Answer: Option (4) is the correct answer.

Explanation:

It is known that on moving down a group there will be decrease in melting point of the element because of increase in number of shells.

As a result, outermost electrons move away from the nucleus due to which there will be decrease in force of attraction between the protons and valence electrons. Hence, there will be decrease in melting point.

Therefore, the given elements are of same group and Rb has largest atomic size.

Thus, we can conclude that Rb has the lowest melting point.

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