1. Alpha Particle Experiment:

When alpha particles are sent through a thin metal foil, only one out of ten thousand of them is rebounded. This observation led to the conclusion that:

a. Positively charged particles are concentrated at the center of the atom.
b. More electrons are revolving around the nucleus of the atom.
c. Unit positive charge is only present in an atom.
d. The massive sphere with a more negative charge and unit positive charge is present at the center of the atom.

2. Canal Ray Experiment:

The canal ray experiment led to the discovery of:

a. Protons
b. Neutrons
c. Electrons
d. Nucleus

3. Energy Difference Between Shells:

In which of the following pairs of shells is the energy difference between two adjacent orbits minimum?

a. K, L
b. L, M
c. M, N
d. N, O

4. Assertion and Reason:

Assertion A: An electron in the inner orbit is more tightly bound to the nucleus.
Reason B: The greater the absolute value of the energy of an electron, the more tightly the electron is bound to the nucleus.

a. Both A and B are true, but B is not the appropriate reason for A.
b. Both A and B are individually correct, and B is the correct reason for A.
c. A is correct, but B is not correct.
d. Both A and B are not correct.

5. Isotopes and Atomic Weight:

If two naturally occurring isotopes of an element are [tex]${ }_7^{15} X$[/tex] and [tex]${ }_7^{11} X$[/tex], what is the percentage composition of each isotope of [tex]$X$[/tex] occurring respectively if the average atomic weight accounts for 14?

a. 95, 5
b. 80, 20
c. 75, 25
d. 65, 35

6. Isotopes and Percentage Abundance:

An element has two isotopes with mass numbers 16 and 18. The average atomic weight is 16.5. The percentage abundance of these isotopes is [tex]$\qquad$[/tex] and [tex]$\qquad$[/tex] respectively.

a. 75, 25
b. 25, 75
c. 50, 50
d. 33.33, 66.67

7. Identifying Isobars:

Which among the following are isobars?

a. [tex]$\quad{ }_b^a X,{ }_b^{a+1} Y$[/tex]
b. [tex]${ }_b^a X,{ }_c^b{ }_c$[/tex]
c. [tex]${ }_b^a X,{ }_{b+1}^a Y$[/tex]
d. [tex]${ }_b^a X ,{ }_{b-1}^{a-1} Y$[/tex]

8. Fractional Atomic Masses:

Some of the elements have fractional atomic masses. The reason for this could be:

a. The existence of isobars.
b. The existence of isotopes.
c. The nuclear reactions.
d. The presence of neutrons in the nucleus.

Certainly! Let's address each part of the question one by one.

1. Alpha Particle Experiment Conclusion:
- When alpha particles are sent through a thin metal foil, only a small fraction (one out of ten thousand) rebound. This led to the conclusion that atoms have a small, dense, positively charged nucleus. Thus, the correct answer is:
- a. Positively charged particles are concentrated at the center of the atom.

2. Canal Ray Experiment Discovery:
- The canal ray experiment led to the discovery of protons. Therefore, the correct answer is:
- a. protons

3. Energy Difference Between Shells:
- The energy difference between adjacent orbits (shells) decreases as you move away from the nucleus. Thus, the minimum energy difference is between:
- d. [tex]$N, O$[/tex]

4. Assertion and Reason:
- The assertion is that an electron in the inner orbit is more tightly bound to the nucleus. The reason states that a greater absolute value of the energy of an electron means it is more tightly bound. Both statements are true, and the reason correctly explains the assertion. Hence, the correct answer is:
- b. Both [tex]$A$[/tex] and [tex]$B$[/tex] are individually correct and [tex]$B$[/tex] is the correct reason for [tex]$A$[/tex].

5. Percentage Composition of Isotopes:
- For the isotopes [tex]${ }_7^{15} X$[/tex] and [tex]${ }_7^{11} X$[/tex], if the average atomic weight is 14, the percentage compositions are:
- b. 80, 20

6. Percentage Abundance of Isotopes:
- An element has isotopes with mass numbers 16 and 18, and the average atomic weight is 16.5. The percentage abundance of these isotopes is:
- a. 75, 25

7. Isobars:
- Isobars are atoms of different elements with the same atomic mass but different atomic numbers. The correct pair of isobars is:
- d. [tex]${ }_b^a X ,{ }_{b-1}^{a-1} Y$[/tex]

8. Reason for Fractional Atomic Masses:
- Fractional atomic masses are primarily due to:
- b. the existence of isotopes.

These answers will help you understand the concepts related to atomic structure and isotopes. If you have more questions or need further clarification, feel free to ask!