The ratio of spacing between the third and fourth orbit to the spacing between sixth andseventh orbit of H-atom is

The spacing between orbits in a hydrogen atom is determined by the formula r = n^2 * a0, where r is the radius of the nth orbit, n is the principal quantum number (the number of the orbit), and a0 is the Bohr radius (approximately 0.529 angstroms).

The spacing between the third and fourth orbits is r4 - r3 = (4^2 - 3^2) * a0 = 7 * a0.

The spacing between the sixth and seventh orbits is r7 - r6 = (7^2 - 6^2) * a0 = 13 * a0.

Therefore, the ratio of the spacing between the third and fourth orbits to the spacing between the sixth and seventh orbits is 7/13.