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A beggar wrapped himself with a few layers of newspaper on a cold winter night. This helped him to keep himself warm because (a) friction between the layers of newspaper produces heat. (b) air trapped between the layers of newspaper is a bad conductor of heat. (c) newspaper is a conductor of heat. (d) newspaper is at a higher temperature than the temperature of the surrounding.

Answer: (b) air trapped between the layers of newspaper is a bad conductor of heat. It's due to the fact that newspaper is an insulator, meaning... View Article

An element X of group 15 exists as a diatomic molecule and combines with hydrogen at 773 K in presence of the catalyst to form a compound, ammonia which has a characteristic pungent smell. (a) Identify the element X. How many valence electrons does it have? (b) Draw the electron dot structure of the diatomic molecule of X. What type of bond is formed in it? (c) Draw the electron dot structure for ammonia and what type of bond is formed in it?

Answer: (a) Element X is Sulphur (b) The electronic configuration of sulphur is written as Sulphur (Z = 16) = 1s2 2s2 2p6 3s2 3p4 = 2, 8, 6 (c)... View Article

An element X which is a yellow solid at room temperature shows catenation and allotropy. X forms two oxides which are also formed during the thermal decomposition of ferrous sulphate crystals and are the major air pollutants. (a) Identify the element X (b) Write the electronic configuration of X (c) Write the balanced chemical equation for the thermal decomposition of ferrous sulphate crystals? (d) What would be the nature (acidic/ basic) of oxides formed? (e) Locate the position of the element in the Modern Periodic Table

Answer: (a) Electropositive nature of the element(s) increases down the group and decreases across the period. Lithium is the most... View Article

(a) Electropositive nature of the element(s) increases down the group and decreases across the period (b) Electronegativity of the element decreases down the group and increases across the period (c) Atomic size increases down the group and decreases across a period (left to right) (d) Metallic character increases down the group and decreases across a period. Based on the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9. (a) Name the most electropositive element among them (b) Name the most electronegative element (c) Name the element with the smallest atomic size (d) Name the element which is a metalloid (e) Name the element which shows maximum valency.

Answer: Mendeleev’s periodic table is an arrangement of elements in an increasing atomic mass order in a tablet form, such that it... View Article

Mendeleev ′ predicted the existence of certain elements not known at that time and named two of them as Eka-silicon and Eka-aluminium. (a) Name the elements which have taken the place of these elements (b) Mention the group and the period of these elements in the Modern Periodic Table. (c) Classify these elements as metals, non-metals or metalloids (d) How many valence electrons are present in each one of them?

Answer: (a) H, He, Li, Be, B, C, N, O, F, Ne, Mg, Al, Si, P, S, Cl, Ar, K, Ca (b) Group 1:H, Li, Na, K Group 2: Be, Mg, Ca Group 13: B. Al Group... View Article

An element X (atomic number 17) reacts with an element Y (atomic number 20) to form a divalent halide. (a) Where in the periodic table are elements X and Y placed? (b) Classify X and Y as metal (s), non-metal (s) or metalloid (s) (c) What will be the nature of oxide of element Y? Identify the nature of bonding in the compound formed (d) Draw the electron dot structure of the divalent halide

Answer: (a) X is in Group 17, period 3 Y is in group 2 Period 4. (b) X is non-metal Y is metal (c) Y Oxide will be basic in nature. The... View Article

An element is placed in 2nd Group and 3rd Period of the Periodic Table, burns in presence of oxygen to form a basic oxide. (a) Identify the element (b) Write the electronic configuration (c) Write the balanced equation when it burns in the presence of air (d) Write a balanced equation when this oxide is dissolved in water (e) Draw the electron dot structure for the formation of this oxide

Answer: (a) Element is Magnesium (b) Electronic Configuration of magnesium is written as The number of electrons for the Mg atom are 12... View Article

Properties of the elements are given below. Where would you locate the following elements in the periodic table? (a) A soft metal stored under kerosene (b) An element with variable (more than one) valency stored underwater. (c) An element which is tetravalent and forms the basis of organic chemistry (d) An element which is an inert gas with atomic number 2 (e) An element whose thin oxide layer is used to make other elements corrosion-resistant by the process of “ anodising”

Answer: (a) A soft metal stored under kerosene - Sodium(Na) [Group 1, Period 3] (b) An element with variable (more than one) valency stored... View Article