Structure of Atom

   To explain his theory , Bohr used

• Conservation of linear momentum      

• Conservation of angular momentum

• Conservation of quantum frequency   

• Conservation of energy

Answer explanation

Bohr's theory of the atom relies on the conservation of angular momentum, which explains the quantized orbits of electrons around the nucleus. This principle is fundamental to understanding atomic structure in quantum mechanics.

   If scattering particles are 56 for 90⁰ angle then this will be at 60⁰ angle

• 224       

• 256

• 98         

• 108

Answer explanation

The scattering particles at 90° is 56. Using the relationship of scattering angles, at 60°, the number of particles increases to 224, which is calculated based on the proportionality of scattering with respect to the angle.

   Energy of electron in a orbit of H-atom is

• Positive        

• Negative

• Zero                 

• Nothing can be said

Answer explanation

The energy of an electron in an orbit of a hydrogen atom is negative. This indicates that the electron is bound to the nucleus, meaning it requires energy to remove it from the atom. Thus, the correct answer is Negative.

  The concept of stationary orbits was proposed by

• Neil Bohr        

• J.J. Thomson           

• Ruther ford           

• I. Newton

Answer explanation

The concept of stationary orbits was introduced by Neil Bohr in his model of the atom, where electrons occupy fixed orbits around the nucleus without radiating energy.

   The ratio of the largest to shortest wavelengths in Lyman series of hydrogen spectra is

• 25/9             

• 17/6                        

• 9/5                     

• 4/3 

Answer explanation

In the Lyman series, the longest wavelength corresponds to the transition from n=2 to n=1, and the shortest to n=infinity to n=1. The ratio of these wavelengths simplifies to 4/3, making it the correct answer.

In which region of electromagnetic spectrum does the Lyman Series of hydrogen atom lie

• Ultraviolet

• Infrared

• Visible

• X-ray                                             

Answer explanation

The Lyman Series corresponds to transitions of electrons in a hydrogen atom that emit ultraviolet light. Therefore, the correct answer is Ultraviolet, as it lies in the ultraviolet region of the electromagnetic spectrum.

Which of the following is the property of Rydberg constant

• It is universal constant          

• it is same for all the hydrogen like atoms

• It depends on the atomic number of the atom

• It depends on the mass number of the atom

Answer explanation

The Rydberg constant is the same for all hydrogen-like atoms because it is derived from the properties of the electron transitions in these atoms, which share similar structures despite differing atomic numbers.

Thomson’s atom model could not explain successfully

• Thermionic emission               

• Photoelectric effect   

• lionization of particles

Answer explanation

Thomson’s atom model, which depicted the atom as a uniform sphere of positive charge with electrons embedded, failed to explain β-particle scattering. This phenomenon demonstrated that atoms have a concentrated nucleus, contradicting Thomson's model.

Rutherford’s experiment on scattering of α- particle shows that the atom

• is positively charged          

• has a very large nucleus       

• is negatively charged

• has a very small positively charged nucleus at the centre

Answer explanation

Rutherford's experiment demonstrated that most of the mass and positive charge of an atom is concentrated in a very small nucleus at the center, which is surrounded by electrons, confirming the atomic structure.

The wavelength of first member of Balmer series is 6563 Å. Calculate the  wavelength of first  member of Lyman series.

• 1215Angstrom    

• 1342 Angstrom    

• 1315 Angstrom    

• 3412 Angstrom

Answer explanation

The Lyman series corresponds to transitions to the n=1 level. The wavelength of the first member (n=2 to n=1) is calculated using the Rydberg formula, yielding 1215 Å, which is the correct answer.