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 correct electronic configuration of Krypton, whose atomic number is 36?
[A] 2, 18,16
[B] 2,8,18,8
[C] 2,18,8,8
[D] 2,8,20,6
Show Answer
Correct Answer: B [2,8,18,8]
Notes:
Krypton is a chemical element with symbol Kr and atomic number 36. It is a member of group 18 (noble gases) elements. The electronic configuration of Krypton is [2, 8, 18, 8]
32. What happens to the atomic radius when one moves from top to bottom in a group of the periodic table?
[A] Increases
[B] Decreases
[C] Remains same
[D] No proper relationship.
Show Answer
Correct Answer: A [Increases]
Notes:
The number of additional energy levels increases as one moves from top to bottom in a group and as a result the distance between nucleus and outer most electron also increases.
33. What is the name of the Ethanol which contains 5% water by volume?
[A] Rectified spirit
[B] Denatured spirit
[C] Methylated alcohol
[D] Power alcohol
Show Answer
Correct Answer: A [Rectified spirit ]
Notes:
A rectified spirit, rectified alcohol, or neutral spirit is highly concentrated ethanol which has been purified by means of repeated distillation, a process that is called rectification. It typically contains 95% alcohol by volume (ABV). Rectified spirits are used in mixed drinks, in the production of liqueurs, for medicinal purposes, and as a household solvent.
34. Which among the following is a covalent compound?
[A] Calcium chloride
[B] Magnesium fluoride
[C] Sodium chloride
[D] Carbon tetrachloride
Show Answer
Correct Answer: D [Carbon tetrachloride]
Notes:Ionic compounds are made up of a metal and non-metal, and covalent compounds are made up of two non-metals forming polar or non-polar covalent compounds. In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedral configuration joined to a central carbon atom by single covalent bond.
- CH4 + 4Cl2 —> CCl4 + 4HCl
35. When cathode rays strike a target of high atomic weight, they give rise to:
[A] D-rays
[B] E and J rays
[C] X-rays
[D] positive rays
Show Answer
Correct Answer: C [X-rays]
Notes:
When cathode rays strike a solid target of high atomic weight and high melting point such as tungsten, molybdenum, etc, they give rise to a highly penetrating radiation called the X-rays.
36. Atoms of different elements have:
[A] same atomic number and same electronic configuration
[B] different atomic number and same eletronic configuration
[C] different atomic number and different number of valence electrons
[D] same number of electrons and neutrons
Show Answer
Correct Answer: C [different atomic number and different number of valence electrons]
Notes:
Each element’s atoms have a different number of protons, neutrons, and electrons, i.e. they have different atomic numbers, difference in valence electrons and other properties. Their reactivity also varies because of the number and activeness of the electrons in the atom.
37. What is formed when helium atom loses one electron?
[A] Proton
[B] Positive helium ion
[C] Negative helium ion
[D] Alpha particle
Show Answer
Correct Answer: B [Positive helium ion]
Notes:
Ions are created when an atom loses or gains an electron. When an atom loses an electron, it becomes a cation (positive ion); when it gains an electron, it becomes an anion. So, when helium atom loses an electron, it becomes positively charged ion, i.e., it becomes a cation.
38. The atoms of the elements having same difference between mass number and atomic number are called:
[A] Isobar
[B] Isotopes
[C] Isotones
[D] None of the above
Show Answer
Correct Answer: C [Isotones]
Notes:
Atomic number is the number of protons present in an atom; while, mass number is the sum of the number of protons and the neutrons of an atom. Isotones are the atoms of different elements which contain same number of neutron with different mass number and atomic number. For example, Silicon and Phosphorous have same number of neutron 16 with different mass number 30,31 and atomic number 14,15.
39. Brass gets discoloured in air due to constant exposure in presence of:
[A] Aluminium phosphide
[B] Hydrogen sulphide
[C] Hydrogenated wafers
[D] Aluminium sulphide
Show Answer
Correct Answer: B [Hydrogen sulphide]
Notes:
Brass gets discoloured in air because of Hydrogen sulphide. Transition elements are coloured. The brass is combination of Zn and Cu. But it is discoloured due to hydrogen sulphide in air with formation of Zns and Cus.
40. Which of the following is very reactive and kept in kerosene?
[A] Sodium
[B] Potassium
[C] Iodine
[D] Bromine
Show Answer
Correct Answer: A [Sodium]
Notes:
Sodium is a very reactive metal. It reacts vigorously both with oxygen and water. A lot of heat is generated in this process. Therefore, it is stored in kerosene to avoid contacts between both atmospheric oxygen and water.
