Concept:For a hydrogen-like ion, the radius of the nth Bohr orbit is given by rn=Z52.9n2pm.Explanation:He+ is a hydrogen-like species with atomic number Z=2.For the first orbit, n=1.Substitute n=1 and Z=2 in the formula:r1=252.9×(1)2pm.r1=252.9=26.45pm.Hence, the radius of the first orbit of He+ is 26.45pm.Answer:26.45pmNone of the given options matches this value exactly.