The radius of a hydrogen atom is 10 10 m. Number of hydrogen atoms necessary to have a length of one nanometre is :

To find the number of hydrogen atoms required to span a length of one nanometre, we must compare the dimensions of the atom with the target length. The radius of a hydrogen atom is given as 10⁻¹⁰ m. The diameter of a single atom is twice its radius, which equals 2 × 10⁻¹⁰ m. A nanometre (nm) is defined as 10⁻⁹ m. To calculate the number of atoms needed to cover this distance, we divide the total length by the diameter of one atom: (10⁻⁹ m) / (2 × 10⁻¹⁰ m). This calculation results in 10 / 2, which equals 5. While some sources suggest a smaller radius of approximately 0.5 Å (0.5 × 10⁻¹⁰ m) for hydrogen, using the specific radius provided in the question (10⁻¹⁰ m) leads directly to the answer of 5 atoms.