Question

Which of the following statements in relation to the solar system is/are correct?

• A. The most abundant elements are H and He.
• B. The abundances of elements with atomic numbers 1-50 show an overall decreasing trend.
• C. The abundances of heavier elements (atomic number >50) are mostly higher than that of lighter elements (atomic number <50).
• D. Elements having odd atomic numbers are more abundant than their immediate neighbours.

Hint:

Hydrogen and helium dominate the solar system, and heavier elements are relatively less abundant.

Answer 1

The Correct Option is A, B

Analyzing solar system elemental abundances:

(A) - Hydrogen (~73% by mass, ~92% by number) and Helium (~25% by mass, ~8% by number) are by far the most abundant elements in the solar system. Together they comprise about 98% of all matter. This reflects the primordial composition from the Big Bang and stellar nucleosynthesis.

(B) - There is a general exponential decrease in elemental abundance with increasing atomic number from H (Z=1) through the first 50 elements. This trend reflects:

• The decreasing efficiency of stellar nucleosynthesis for heavier elements
• The exponentially greater energy required to fuse heavier nuclei
• While there are local variations (peaks and valleys), the overall trend from Z=1 to Z=50 is strongly decreasing

(C) - This is false. Elements heavier than iron (Z=26) and certainly those above Z=50 are significantly less abundant than lighter elements. Heavy elements (>50) are produced through slow and rapid neutron capture processes (s-process and r-process) which are much rarer than the fusion processes creating lighter elements. The abundances continue to decrease for heavier elements.

(D) - This is the opposite of reality. The Oddo-Harkins rule states that elements with even atomic numbers are generally more abundant than their odd-numbered neighbors. This occurs because:

• Even-Z nuclei have paired protons, making them more stable
• Stellar nucleosynthesis favors production of even-Z elements through alpha-particle capture
• Odd-Z elements show lower abundances due to lower nuclear stability

Answer: (A) and (B) are correct