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301.	The metallic luster exhibited by sodium is explained byA. existence of body centered cubic latticeB. excitation of free electronsC. diffucion of sodium ionsD. oscillation of loose electrons
Answer» Correct Answer - D the oscillation of loose electrons in metallic sodium is responsible for metalic lustre.

302.	Soda lime is a mixture ofA. `NaOH and CaCO_(3)`B. `Na_(2)CO_(3) and CaCO_(3)`C. NaOH and CaOD. `NaOH and Ca(OH)_(2)`
Answer» Correct Answer - C Quick lime (CaO) slaked with soda`(NaOH)` given a solid, soda lime.

303.	The product obtained on fusion of `BaSO_(4)` and `Na_(2)CO_(3)` isA. `BaCO_(3)`B. BaOC. `Ba(OH)_(2)`D. `BaHSO_(4)`
Answer» Correct Answer - A `BaSO_(4)_Na_(2)CO_(3)overset("Fusion")rarrBaCO_(3)+Na_(2)SO_(4)`

304.	The fusion mixture is a mixture ofA. `NaHCO_(3) " and " KHCO_(3)`B. `Na_(2)CO_(3) " and " K_(2)CO_(3)`C. `NaHCO_(3) " and " K_(2)CO_(3)`D. `Na_(2)CO_(3) " and " KHCO_(3)`
Answer» Correct Answer - B it is a mixture of anhydrous sodium ad potassium carbonates `Na_(2)CO_(3)` and `K_(2)CO_(3)`.

305.	Which of the following is incorrect about sodium carbonate ?A. With hot milk of lime, it reacts to form sodium hydroxideB. It reacts with dilute mineral acids evolving `CO_(2)(g)`C. It undergoes hydrolysis to form an acidic solutionD. None of these
Answer» Correct Answer - C Being a salt of a strong base (NaOH) and weak acid `(H_(2)CO_(3))`, when dissovled in water, sodium carbonate undergoes hydrolysis to form an alkaline solution. ,brgt `Na_(2)CO_(3)+2H_(2)OhArrH_(2)CO_(3)+2NaOH` or `CO_(3)^(2-)+2H-OHhArrH_(2)CO_(3)+2OH^(-)` ltbr Milk of lime is a suspension o line in water. (1) `Na_(2)CO_(3)+Ca(OH)_(2)toCaCO_(3)darr+2NaOH` (2). `NaCO_(3)+2HCl to 2NaCl+H_(2)O+CO_(3)uarr`

306.	Explain the trends in the solubility of carbonates , sulphates and hydroxides of alkaline earth metals.
Answer» The solubility, thermal stability and basic character of hydroxides increase with increasing atomic number from `Mg(OH)_(2)` to `Ba(OH)_(2)`.

307.	The main pigment for the absorption of light in green plants is chlorophy II-a which containsA. BeB. MgC. CaD. Sr
Answer» Correct Answer - B In chlorophyll, Mg is the center of a flat heterocyclic organic ring system called porphyrin, in which 4 nitrogen atoms are bonded to Mg.

308.	In curing cement plasters, water is sprinkled from time to time. This helps inA. keeping it coolB. hydrated sand gravel mixed with cementC. developing interlocking needle-like crystals of hydrated silicatedD. converting sand into silicic acid
Answer» Correct Answer - C Interlocking needle-like crystals of hydrated silicates are developed by sprinking water from time to time.

309.	`KO_(2)` is used in oxygen cylinders in space and submarines because itA. produces ozoneB. absorbs `CO_(2)`C. eliminates moistureD. absorbs `CO_(2)` and increase `O_(2)` content
Answer» Correct Answer - D `KO_(2)` is used in space capsules, submarines, and breathing masks because it both produces oxygen and removes carbon dioxide. Both function are important in life support systems: `4KO_(2)+2CO_(2)rarr2K_(2)CO_(3)+3O_(2)` `4KO_(2)+4CO_(2)+2H_(2)Orarr4KHCO_(3)+3O_(2)`

310.	In view of their low ionisation energies, the alkali metals areA. weak oxidizing agentsB. strong reducing agentsC. strong oxidizing agentsD. weak reducing agents
Answer» Correct Answer - B Due to low ionization energies, alkali metals possess a strong tendency to lose electrons. Hence, they act as strong reducing agents.

311.	Which of the following is soluble in organic solvents like ethanol ?A. LiCIB. NaCIC. KCID. RbCI
Answer» Correct Answer - A When a cation approaches an anion, the `e^(-)` cloud of the anion is attracted towards the cation and gets distorted. This effect is called polarization. The greater the polarization, the more the concentration of electrons between the two atoms, the lesser the ionic character while the greater the covalent character. The smaller the cation (for a given anion), the greater is its polarizing power and, hence, the larger is the covalent character. Thus, the covalent character decreases as the size of the cation increases : `LiCI gt NaCI gt KCI gt RbCI gt CsCI` Thus, LiCI with maximum covalent character is soluble in ethanol, acetone, and ethy I accetate. It is also soluble in pyri-dine.

312.	Some of the Group 2 metal halides are covalent and soluble in organic solvents. Among the following metal halides, the one which is soluble in ethanol isA. `BeCl_(2)`B. `MgCl_(2)`C. `CaCl_(2)`D. `SrCl_(2)`
Answer» Correct Answer - A Beryllium halides are essentially covalent and soluble in organic solvents like ethanol.

313.	Which of the following peroxides is not known ?A. `BaO_(2)`B. `SrO_(2)`C. `CaO_(2)`D. `BeO_(2)`
Answer» Correct Answer - D Peroxides are formed by group 2 elements wit increasing case and increasing stability as metal ions become larger because large cations stabilize lage anions by providing high lattice enthalpy. `BaO_(2)` is formed by passing air over `BaO` at `500^(@)C.SrO_(2)` is formed similarly but requires relatively higher temperature and pressure. `CaO_(2)` with `H_(2)O_(2)` and then dehydrating the product. Crude `MgO_(2)` is alos made using `H_(2)O_(2)` but no peroxide of Be is known,

314.	All alkali metal peroxides contain the `[-O-O]^(2-)` ion. They areA. diamagnetic and are colored compoundsB. paramagnetic and are colored compoundsC. paramagnetic and are oxidizing agentsD. diamagnetic and are oxidizing agents
Answer» Correct Answer - D They are diamagnetic as all the electrons are paired, They act as oxidizing agents because they react with water and acid giving hydrogen peroxide : `Na_(2)O+2H_(2)O to 2NaOH+H_(2)O_(2)` They may be regarded as salts of the dibasic acid `H_(2)O_(2)`. They are all colorless compounds except `Na_(2)O_(2)` which is pale yellow in color. Sodium peroxide is widely used as an oxidizing agent in inorganic chemistry.

315.	All alkali metal superoxides contain the ion `[O_(2)]`. They areA. paramagneticB. colored compoundsC. oxidizing agentsD. all of these
Answer» Correct Answer - D Superoxides are paramagnetic because the ion `[O_(2)]^(-)` has an unparied electron. (Refer to molecular orbital theory in Chapter 4.) They are all colored :`LiO_(2) " and " NaO_(2) " are yellow " , KO_(2) " is orange ", RbO_(2) " is brown, and " CsO_(2)` is orange. They are even stronger oxidizing agents than peroxides as they give both `H_(2)O_(2) " and " O_(2)` with either water or acid: `KO_(2)+2H_(2)O to KOH+H_(2)O_(2)+(1)/(2)O_(2)`

316.	Write Lewis structure of `O_(2)^(-)` ion and find out oxidation state of each oxygen atom? What is the average oxidation state of oxygen in this ion?
Answer» The Lewis structure of `O_(2)^(-)` is `:overset(..)underset(.)(O)-ddot(O):^(-)` Oxygen atom carrying no charge has six electrons, so its oxidation number is zero. But oxygen atom carrying -1 charge has 7 electrons, so its oxidation number is -1 Average oxidation number of each oxygen atom `= (1)/(2)` `O_(2)^(-) = 2x =- 1` `x =- (1)/(2)`

317.	`Be` and `Mg` atoms do not impart colour to the flame.
Answer» All alkaline earth metals (except Be and Mg) impart a charactertistic colour to the Bunsen flame. The different colours arise due to different energies required for electronic excitation and de-excitation. Be and Mg atoms due to their small size, bind their electrons more stronly (because of higher effective nuclear charge). Hence, require high exciation energy and are not excited by the energy of the flame with the result that no flame colour is shown by them.

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