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- Question
An atom has 7 electrons in its M - shell and contains 18 neutrons in its nucleus. What is its mass number
Options- A. 25
- B. 27
- C. 35
- D. 43
- Correct Answer
- 35
ExplanationAccording to Bohr model, Each shell can occupy 2 electrons in their orbits where n=1,2,3.. for K,L,M,..
The atom has 2 electrons in k, 8 electrons in L and 7 electrons in M = 2 + 8 + 7 = 17
And given that its nucleus has 18 neutrons
=> its mass number = number of (electrons + neutrons ) = 17 + 18 = 35
- 1. Which one of the following elements is essential for construction is nuclear reactors
Options- A. Cobalt
- B. Nickel
- C. Zirconium
- D. Tungsten Discuss
- 2. The absolute value of charge on electron was determined by
Options- A. J.J.Thomson
- B. R.A. Millikan
- C. Rutherford
- D. Chadwick Discuss
- 3. Sodium carbonate crystal lose water molecules this property is called
Options- A. hygroscopy
- B. deliquescence
- C. efflorescence
- D. None of these Discuss
- 4. Which one of the following substances does not have a melting point
Options- A. bromine
- B. sodium chloride
- C. mercury
- D. glass Discuss
- 5. Which one of the following mixture is homogeneous
Options- A. starch and sugar
- B. methanol and water
- C. graphite and charcoal
- D. calcium carbonate and calcium bicarbonate Discuss
- 6. How many electrons are there in Na+
Options- A. 1
- B. 10
- C. 11
- D. 12 Discuss
- 7. ' Misch metal ' is widely used in manufacture of which of the following
Options- A. Material of car brake
- B. Smoke detectors
- C. Cigarette lighters
- D. Emergency lights Discuss
- 8. Which one of the following elements is the poorest conductor of heat
Options- A. sodium
- B. lead
- C. zinc
- D. mercury Discuss
- 9. When water freezes its density
Options- A. decreases
- B. remains constant
- C. increases
- D. become zero Discuss
- 10. How many moles are there in 140g of Si (atomic mass of silicon is 28)
Options- A. 5
- B. 10
- C. 28
- D. 140 Discuss
Chemistry problems
Search Results
Correct Answer: Zirconium
Correct Answer: R.A. Millikan
Correct Answer: efflorescence
Correct Answer: glass
Correct Answer: methanol and water
Correct Answer: 10
Correct Answer: Cigarette lighters
Correct Answer: lead
Correct Answer: decreases
Explanation:
When water freezes its density decreases.
Water at ordinary temperatures contracts and increases in density as it is cooled, like most substances. But at about 4°C it reaches a maximum density and then decreases in density as it approaches the freezing point.
Correct Answer: 5
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