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Disorders of the Digestive System - Causes, Symptoms & Treatment Disorders of the Digestive System: Causes, Symptoms, Treatment & Prevention 1. Introduction to Digestive Disorders The digestive system breaks down food and absorbs nutrients. Disorders like acid reflux, IBS, or ulcers can interfere with these processes. Understanding symptoms, causes, and treatments is essential for maintaining gut health. 2. Common Digestive System Disorders Acid Reflux (GERD): Stomach acid flows into the esophagus causing heartburn. Peptic Ulcers: Open sores in the stomach or small intestine. Irritable Bowel Syndrome (IBS): Affects bowel habits with cramping and bloating. Constipation: Infrequent or painful bowel movements. Diarrhea: Loose, frequent stools. Inflammatory Bowel Disease (IBD): Includes Crohn's disease and ulcerative colitis. Gallstones: Block bile flow, causing pain an...
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Class 9 Chemistry chapter 2: Atomic Structure - Mcqs Answers

 

MCQs with Explanations for Chemistry Students 

Understanding chemistry concepts requires not just memorization but also clear reasoning. Here are multiple-choice questions (MCQs) with detailed explanations to help students grasp key chemistry topics effectively.

1. How many electrons can fit in the third shell of an atom?

(a) 8
(b) 18 ✅
(c) 10
(d) 32

Explanation:

The maximum number of electrons in a shell is determined by the formula 2n², where n is the shell number.

For the third shell (n = 3):
→ 2(3²) = 2 × 9 = 18 electrons

Thus, the third shell can hold a maximum of 18 electrons.

2. What did scientists learn from the discharge tube experiment?

(a) The structure of the atom
(b) The discovery of neutrons and protons
(c) The discovery of electrons and protons ✅
(d) The presence of a nucleus in an atom

Explanation:

The discharge tube experiment (by J.J. Thomson) helped discover electrons and their negative charge. When high voltage was passed through a gas in a sealed tube, a stream of cathode rays (electrons) was observed, proving their existence.

3. Why are isotopes not listed separately in the periodic table?

(a) The table cannot fit all isotopes
(b) Some isotopes change into different elements
(c) Isotopes have the same atomic number ✅
(d) Isotopes do not follow periodic trends

Explanation:

Isotopes of an element have the same number of protons (same atomic number) but different numbers of neutrons. Since the periodic table is arranged by atomic number, isotopes of the same element are grouped together under one place.

4. Which particle differs in the isotopes of an element?

(a) Electron
(b) Neutron ✅
(c) Proton
(d) Both neutron and electron

Explanation:

Isotopes have the same number of protons and electrons but different numbers of neutrons. For example:

  • Carbon-12 has 6 neutrons
  • Carbon-14 has 8 neutrons

Since protons determine an element’s identity, only neutrons vary among isotopes.

5. What is the boiling point of heavy water (D₂O)?

(a) 101.4°C ✅
(b) 98.2°C
(c) 100°C
(d) 105.4°C

Explanation:

Heavy water (D₂O) contains deuterium (²H) instead of hydrogen (¹H). Deuterium is heavier than hydrogen, making the molecular bonds stronger, which raises the boiling point to 101.4°C, slightly higher than regular water (100°C).

6. Given that hydrogen has two isotopes with abundances 99.9844% and 0.0156%, what is its relative atomic mass?

(a) 1.0078 ✅
(b) 1.0784
(c) 1.0800
(d) 1.0700

Explanation:

The relative atomic mass is calculated as:


(1.0078 \times 99.9844\%) + (2.0141 \times 0.0156\%)


= (1.0078 \times 0.999844) + (2.0141 \times 0.000156)


≈ 1.0078

7. How does radiocarbon dating help archaeologists?

(a) Determines the age of organic matter ✅
(b) Finds the composition of matter
(c) Measures usefulness of matter
(d) Checks if matter is radioactive

Explanation:

Radiocarbon dating uses Carbon-14 (¹⁴C) to measure the age of ancient organic materials (bones, plants, fossils). Since ¹⁴C decays over time, scientists can compare the amount left in a sample to determine its age.

8. What force holds particles in the nucleus together?

(a) Strong nuclear force ✅
(b) Weak nuclear force
(c) Electrostatic force
(d) Dipolar force

Explanation:

Protons are positively charged, and they should repel each other. However, the strong nuclear force binds protons and neutrons together, keeping the nucleus stable. This force is the strongest in nature but works only at very short distances.

9. Why don’t electrons fall into the nucleus?

(a) They stay still
(b) They revolve around the nucleus ✅
(c) They have wave-like nature
(d) A magnetic field pushes them away

Explanation:

Electrons revolve around the nucleus due to their kinetic energy, preventing them from collapsing into the positively charged nucleus. This balance of attractive and centrifugal forces keeps electrons in stable orbits.

10. Rubidium has two isotopes: 85Rb (72.2% abundance) and 87Rb. What is the abundance of 87Rb if the atomic mass is 85.47?

(a) 15%
(b) 28%
(c) 37% ✅
(d) 72%

Explanation:

Using the formula for relative atomic mass:


Atomic Mass= 85 Rb/ 85 + 87 Rb/87

Given:


85.47 = (72.2/85) + (x/87)

Solving for x (abundance of 87Rb):


85.47 = (0.722/85) + (x/87)


85.47 = 61.37 + 87x


87x = 85.47 - 61.37


87x = 24.1


x = 24.1/87 = 0.277 = 27.7% approx37%

Thus, the abundance of 87Rb is 37%.

Conclusion

These MCQs with explanations ensure that students not only memorize answers but also understand the logic behind them. Strengthen your chemistry skills by practicing with Chemcore910



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