Question

Which of the following alkali metals has the lowest melting point?

• A. Cs
• B. Li
• C. Na
• D. K

Hint:

Remember that in Group 1, the metal with the largest atomic size will have the lowest melting point due to weaker metallic bonding.

Answer 1

The Correct Option is A

Step 1: Recall the melting point trend.
For alkali metals in Group 1, the melting point falls as we move down the group. So the metal lowest in the group melts most easily.
Step 2: Why the trend happens.
As we go down the group the atoms get bigger. Bigger atoms hold their metallic bonds more weakly, so less heat is needed to melt them.
Step 3: Order the given metals.
The order in the group from top to bottom is Li, then Na, then K, then Cs. So Cs is the lowest of the four.
Step 4: Compare their sizes.
Caesium has the largest atom of these four. So it has the weakest metallic bond among them.
Step 5: Link size to melting point.
Weakest bond means the lowest melting point. So caesium melts at the lowest temperature of the four.
Step 6: Final choice.
The alkali metal with the lowest melting point here is caesium.\[ \boxed{\text{Cs}} \]