General Science Chemistry MCQs
Chemistry Objective (Multiple Choice) General Knowledge Questions & Answers for SSC-CGL, UPPSC, UPSC, NDA, CDS and UPSC Civil Services Prelims Examination
31. Which of the following is also known as Alumina?
[A] AlO2
[B] Al2O3
[C] Al2O4
[D] Al2CO2
Show Answer
Correct Answer: B [Al2O3]
Notes:
Alumina is the common name given to aluminum oxide (Al2O3). It is produced from bauxite to get pure aluminium metal.
32. What is the relation between mass and wavelength of any matter, as per de Broglie’s relation?
[A] Both are directly proportional
[B] Both are inversely proportional
[C] Both are independent of each other
[D] wavelength is twice the square of the mass
Show Answer
Correct Answer: B [Both are inversely proportional]
Notes:
According to de Broglie, every object in motion has a wave character. As per de Broglie’s relation, mass and wavelength are inversely proportional to each other.
33. How many values an Electron spin quantum number can have?
Show Answer
Correct Answer: B [2]
Notes:
Electron spin quantum number is used to determine the orientation of the spin of the electron. It can have two values +1/2 and -1/2. +1/2 identifies the clockwise spin and -1/2 identifies the anti- clockwise spin.
34. Which of the following is correct about effective nuclear charge experienced by the orbital?
[A] it increases with increase of azimuthal quantum number
[B] it increases with increase of magnetic quantum number
[C] it decreases with increase of azimuthal quantum number
[D] It is same everywhere
Show Answer
Correct Answer: C [it decreases with increase of azimuthal quantum number]
Notes:
Because of the screening effect, the net positive charge experienced by the electron from the nucleus is lowered and is known as effective nuclear charge. Effective nuclear charge experienced by the orbital decreases with increase of azimuthal quantum number(l).
35. What will be the number of neutrons in an atom having atomic number 35 and mass number 80?
Show Answer
Correct Answer: B [45]
Notes:
The total number of nucleons is termed as mass number (A) of the atom. In this case, mass number is 80. Therefore, sum of the number of neutrons and protons is 80. As atomic number is 35, we know that number of protons is 35. Hence, number of neutrons = 80-35 = 45.
36. Which of the following is true about Rutherford model of atom?
[A] it explains how the electrons are distributed around the nucleus
[B] It cannot explain about the stability of an atom around the nucleus
[C] It tells us about the energies of the electrons around the nucleus
[D] All of the above
Show Answer
Correct Answer: B [It cannot explain about the stability of an atom around the nucleus]
Notes:
A serious limitation of the Rutherford model is that it says nothing about the electronic structure of atoms i.e., how the electrons are distributed around the nucleus and what are the energies of these electrons. Also, the Rutherford model cannot explain the stability of an atom.
37. What do we call an ideal body which emits and absorbs all frequencies?
[A] Black body
[B] White body
[C] Red body
[D] Zero body
Show Answer
Correct Answer: A [Black body]
Notes:
An ideal body, which emits and absorbs all frequencies is known as a black body. The radiation emitted by such a body is called black body radiation.
38. Which of the following statements is correct about Beta-decay?
[A] In β+decay, Mass number increases by 2
[B] In β−decay, Mass number decreases by 2
[C] In β−decay, the atomic number increases by 1
[D] None of the above
Show Answer
Correct Answer: C [In β−decay, the atomic number increases by 1]
Notes:
In both β− and β+ decay, the mass number A remains unchanged. In β− decay, the atomic number of the nucleus goes up by 1, while in β+ decay, the atomic number goes down by 1.
39. Which of the following alpha-emitter is commonly used in smoke detectors?
[A] Bismuth – 209
[B] Amrecium-231
[C] Uranium-238
[D] Protactinium-231
Show Answer
Correct Answer: B [Amrecium-231]
Notes:
Americium-241 is an isotope of americium. It is the most common isotope of americium having a half-life of 432.2 years. It is radioactive and is commonly used in ionization type smoke detectors.
40. What do we call the reactions in which there is an exchange of ions between the reactants?
[A] Double Displacement reaction
[B] Decomposition reaction
[C] Displacement reaction
[D] Combination reaction
Show Answer
Correct Answer: A [Double Displacement reaction]
Notes:
The reactions in which there is an exchange of ions between the reactants are called double displacement reactions.
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