Two isotopes of Boron are found in the nature with atomic weights 10.01(I) and 11.01(II). The atomic weight of natural Boron is 10.81. The percentage of (I) and (II) isotopes in it are respectively-

(A) 20 and 80

(B) 10 and 90

(C) 15 and 75

(D) 30 and 70

There are three energy levels in an atom. How many spectral lines are possible in its emission spectra?

1. One

2. Two

3. Three

4. Four

The increasing order of energy of electromagnetic radiation can be represented as:

Mass of neutron is ........................times the mass of electron-

(A) 1840

(B) 1480

(C) 2000

(D) None

Which of the following species has more number of electrons in comparison with the neutrons?

1. Al³⁺

2. O^2-

3. F^-

4. C

The ratio of the difference in energy between the first and second Bohr orbit to that between the second and the third Bohr orbit of hydrogen is -

1. 1/2

2. 1/3

3. 4/9

4. 27/5

The radius of second stationary orbit in Bohr's atom is R. The radius of 3^rd orbit will be:-

1. 9R

2. R/4

3. 9R/4

4. 2R

Bohr's model is not valid for:-

(1) H-atom

(2) D-atom

(3) T-atom

(4) He-atom

Which of the following pairs of d-orbitals will have electron density along the axes?

1.  d_z²,d_xz

2.  d_xz,d_yz

3.  d_z²,d_x²-y²

4.  d_xy,d_x²-y²

Which is the correct order of increasing energy of the listed orbitals in the atom of titanium?

(1) 3s 4s 3p 3d                   

(2) 4s 3s 3p 3d

(3) 3s 3p 3d 4s                   

(4) 3s 3p 4s 3d