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Q7 (CDS-II/2008) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Periodic table elements Answer Verified

Which one of the following is the softest ?

Result
Your answer: —  Â·  Correct: A
Explanation

Among the given options, sodium is the softest metal. Sodium and lithium are both alkali metals (Group 1), which are characterized by being soft enough to be cut with a knife [2]. In contrast, aluminium and iron are transition or post-transition metals that, while malleable, are significantly harder and do not share this property [2]. Within the alkali metal group, hardness decreases as you move down the group because the metallic bonding becomes weaker as the atomic size increases. Consequently, sodium (atomic number 11) is softer than lithium (atomic number 3). Quantitative data confirms this trend, with sodium having a lower Mohs hardness value (0.5) compared to lithium (0.6). Therefore, sodium is the softest of the four metals listed.

Sources

  1. [2] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > Table 3.1 > p. 40
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