Parents and students of SSC Class 10 are concerned after a question in the Science-I examination caused confusion. The question, worth one mark, asked for the name of the atom with the smallest size. Some students confidently wrote "hydrogen" based on their scientific knowledge. However, upon learning that others wrote "helium," panic spread among students and parents.
The concern arose from the possibility that students who chose hydrogen might lose marks despite having the scientifically correct answer. However, the 10th SSC Science textbook does not explain this. Half of them wrote hydrogen, and half wrote helium because the textbook does not provide an answer.
Dr. Kalpana Gangaramani, Founder & MD of Target Publications Pvt Ltd, expressed concern that many students in their Science I SSC board exams feel that they might lose marks for correctly identifying hydrogen as the smaller atom. Some students were confused about who had written helium, but in NCERT, as well as the NASA website, it is mentioned that hydrogen is the smallest atom.
"Scientifically, the calculated value of the atomic radius of hydrogen is 53 pm while the calculated value of the atomic radius of helium is 31 pm. That is because we expect the atomic radius to decrease when we move across the period from left to right. However, hydrogen is a diatomic gas while helium is a monoatomic gas. So, it is not appropriate to compare calculated values of atomic radii. Comparing van der Waals radii of both atoms would be more appropriate. The van der Waals radius of a hydrogen atom is 120 pm while the van der Waals radius of a helium atom is 140 pm. In this case, hydrogen is the smallest atom in the modern periodic table. Hence, I feel that the board should consider awarding marks to students who write hydrogen in their answer," said Gangaramani.