Roman Saini is teaching live on Unacademy Plus
Chemistry MCQs Based on Class XI NCERT
121. The atomic number of the element present in the third period and 17TH group of the periodic table will be? 3 ) 17 8 a) c) d)
Solution: b Explanation: There are two elements in the 1st period and eight elements in the 2nd period., The third period starts with the element with Z (Atomic number) = 11 (Sodium). Now, there are nine elements in the third period. Thus, the 3rd period ends with the element with Z = 18(Argon) i.e. the element in the 18th group of the third period has Z= 18, Hence, the element in the 17th group of the third period has atomic number Z = 17 ,Chlorine(CI) with atomic mass 35.453, which is a p block element.
122. Why do elements in the same group of a periodic table have similar physical and chemical properties? ) The elements in the same group have same atomic number. b) The elements in the same group have same atomic mass. o The elements in the same group have similar number of valance electrons in their outermost shell. a The elements in the same group have same number of electrons.
Solution: c Explanation: The elements in the same group has similar number of valence electrons. They have identical number of electrons in their outermost shell. e.g. All the alkali metals in Group 1 have 1 valence electron, so they all tend to react the same way with other substances.
123. What does atomic radius means? ) Radius of the nucleus of the atom. Distance between protons in the atom. Mean distance between center of nucleus and the boundary of protons. ) Mean distance between the center of nucleus to the boundary of surrounding electrons.
Solution: d Self Explanatory
124. If we go down in a group of the periodic table, the atomic radius will? a. Decrease b. Increase c. Remain constant d. No regular pattern is observed
Solution: b o As we go down in a group, the atomic number of element increases. As more number of electrons are added so more number of orbits are required to accommodate them, hence the bigger radius.
125. How does atomic radius vary in a period of periodic table? a Decreases a. b. Remains same c. d No pattern available d.
Solution: a o Explanation: Atomic radius decreases across a period because valence electrons are being added to the same energy level, at the same time the nucleus is increasing in protons. The increase in nuclear charge attracts the electrons more strongly, pulling them closer to the nucleus.
126. What is meant by the ground state of an atom? It is the highest energy state of an atom. b) It is the mean energy state of an atom. o It is the state in which atoms remain grounded. ) It is the lowest energy state of an atom.
127. Which of the following element has four electrons in its outermost orbit? ) Hydrogen b Oxygen o Helium a) Carbon
Solution: d Explanation: Hydrogen has 1, Helium has 2 and Oxygen has 2 electrons in their outermost orbit.
Solution: c e Self explanatory
Solution: d Explanation: Fluorine is the most reactive non-metal on periodic table. o E It exists in gaseous form at room temperature and even reacts with glass. So, it is almost impossible to store it in pure form and caesium is the most reactive metal.
130. The most reactive metal in the periodic table is? o) Caesium Radium o Fluorine o) Hydrogen b) o Hydrogen
Solution: a Explanation: Caesium is the most reactive metal. It rapidly reacts with water to form Caesium Hydroxide and Hydrogen gas.
131. The least reactive element is Hydrogen b) Beryllium o) Aluminum d) Helium
Solution : c Explanation: Aluminum lodide is formed on the reaction of Aluminium and lodine. Aluminum has three electrons to donate, to become stable and lodine requires 1 electron to stabilize. So, three Iodine atoms will get there electrons from Aluminum to form a stable compound o thco fgo wil from Aluminum to form a Al3+ is highly charged in nature and it can polarize the electron clouds of Cl to a large extent. So, electrons get shared between the two ions. Hence the compound is a covalent one, but the bond is polar covalent Concepts like these help us understand why SO2 exists in nature but not SO10
Solution: c e Self explanatory
o Solution: c Explanation e See the structure of methane SH molecule in the figure 109"
Solution: a Explanation: o In a molecule as we increase the number of electrons shared between two atoms, there will be an increase in bond order, also there will be an increase in the strength of the bond and decrease the distance between nuclei.
136. What is the type of chemical bond formed between Sulphur and Oxygen in Sulphur Dioxide gas? lonic Bond b) Covalent bond o Metallic bond o Hydrogen bond a)
Solution: d Explanation: In physical chemistry, the Van der Waals forces, named after Dutch scientist Johannes Diderik Van der Waals are distance dependent interactions between atoms. e Van der Waals interaction is the weakest of all intermolecular attractions between molecules.
Solution: a Liquefied petroleum gas or liquid petroleum gas (LPG or LP gas), also referred to as simply propane or butane are flammable mixtures of hydrocarbon gases used as fuel in heating appliances, cooking equipment and vehicles Propane and butane haves pane and butane have sigma bond i.e. single bond between carbon atoms. The single black dash represent sigma or the single bond.
140. At high pressure and low temperature intermolecular forces between gas molecules are? a Weak b) Strong o No effect on them d None of these
Solution: b Explanation: At high pressure and temperature, molecules of matter come close to each other making the forces strong.
141. If there is a change in the state of matter, then the chemical properties of the matter will? Change ) Remain constant e Few properties will change, few will not. Data is insufficient.
146. If in a flask, there are three gases, 1 mole Carbon dioxide, 3 mole Helium, and 1 mole Sulphur dioxide. They exert pressure P1, P2 and P3 respectively, the total pressure of the flask will be? Harmonic mean of P1, P2 and P3 b Geometric mean of P1, P2 and P3 o Arithmetic mean of P1, P2 and P3 d) Sum of P1, P2 and P3
Solution: a Explanation: The equation is valid for ideal gas which is a hypothetical gas whose molecules occupy negligible space and have no interactions. Although, this kind of gas does not exist but still the equation PVEnRT holds good for all types of gases. P = pressure of the gas V- volume of gas N-number of moles of gas R- gas constant T= Temperature of the gas
Solution: b Explanation: The lowest possible temperature, or absolute zero as it is called, is -459.67 degrees Fahrenheit, or -273.15 degrees Celsius. It is also called 0 degrees Kelvin, a temperature scale with increments equivalent to degrees of Celsius, but uses absolute zero rather than water's freezing point as its starting point. Absolute zero is the lower limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reaches its minimum value, taken as 0.
150. If we drop few drops of orange juice on blue litmus paper, it will turn? a Green b) Black e) Red d) Remain same in color
Solution: c Explanation: Orange juice is acidic in nature. Mostly sour fruits are acidic. So, it will turn blue litmus red.