The atomic masses of Li and K are 7 and 39, respectively. According to law of triads the atomic mass of Na will be:
Correct answer: A. 23.
- A. 23.
- B. 32.
- C. 46.
- D. 64.
Explanation
According to the law of triads, when elements are grouped into sets of three with similar properties, the atomic mass of the middle element should be roughly the arithmetic mean of the atomic masses of the other two elements. Here, Lithium (Li) and Potassium (K) have atomic masses of 7 and 39, respectively. Therefore, the arithmetic mean is calculated as (7 + 39) / 2 = 46 / 2 = 23, which aligns with the atomic mass of Sodium (Na). Thus, Option A is correct.Options B, C, and D do not match this mean. Option B (32) and D (64) are arbitrary and do not fit the calculation, while Option C (46) mistakenly represents the sum rather than the mean of the atomic masses.
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About Periodic Properties and Trends
Periodic properties arise from electron configuration and effective nuclear charge, producing trends in atomic and ionic radius, ionization energy, electron affinity, electronegativity, metallic character and reactivity. Comparisons run across periods and down groups, with attention to common exceptions. The topic also relates these trends to the behavior of s-block and p-block elements.
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