When the atoms of gold sheet are bombarded with a beam of $\alpha$ -particles, only a few a-particles get deflected where as most of them go straight undeflected. This is because

(A) The force of attraction on the $\alpha$-particles by the oppositely charged electron is not sufficient

(B) The nucleus occupies much smaller volume as compared to the volume of atom

(C) The force of repulsion on fast moving $\alpha$-particles is very small.

(D) The neutrons in the nucleus do not have any effect on $\alpha$-particles

The brackett series of spectral lines arise when an electron in an excited hydrogen atom jumps from an energy level

(1) n=5 to n=1

(2) n=5 to n=3

(3) n=5 to n=4

(4) n=5 to n=2

The ratio of the wavelengths of last lines of Balmer and Lyman series is-

(A) 4:1

(B) 27:5

(C) 3:1

(D) 9:4

Frequency ratio between violet (400nm) and red (750nm) radiations in the visible spectrum, is-

(1) 8/15

(2) 4/15

(3) 15/8

(4) None of these

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