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The correct option is (b) 4Al + 3O2 → 2Al2O3

Best explanation: 4Al + 3O2 → 2Al2O3 is a balanced REACTION because the number of ATOMS of different elements on both sides is equal. The correctly balanced equations of the rest are 2H2 + O2 → 2H2O; Mg(OH)2 + 2HNO3 → Mg(NO3)2 + 2H2O and N2 + 3H2 → 2NH3.

Correct CHOICE is (b) Avogadro’s number

The explanation is: Avogadro number DENOTED by NA. Its VALUE is 602213670000000000000000, also written as 6.022×10^23. It’s the number of ENTITIES in 1 mol of a substance. The units may be electrons, atoms, ions, or molecules, depending on the NATURE of the substance.

The correct OPTION is (a) Properties, mass

For explanation I would SAY: According to DALTON’s Atomic Theory, All ATOMS of a given ELEMENT have identical properties, including identical mass. The reason behind this is that they belong to the same element (here “they” is about atoms).

The correct choice is (d) a UNIFIED mass UNIT, 1.660539040(20)×10^−27kg

For EXPLANATION: Dalton is also known as the unified mass unit that is equal to 1.660539040(20)×10^−27kg or 931.4940954(57)MeV/c^2 or 1822.888486192(53)me (symbol: u, or Da or AMU). It’s a standard unit of mass on the molecular and atomic scale.

Correct choice is (d) A GIVEN compound always contains ABSOLUTELY the same PROPORTION of elements by weight

For explanation I WOULD say: When Joseph Proust worked about the composition of elements present in a compound experimentally, he found out that it was the same for all the samples he TOOK. Joseph Louis concluded that from any source, a particular compound always contains the same elements in the same proportion by mass/weight.

The CORRECT option is (a) Solids

Best EXPLANATION: Solids occupy particular and definite shape and size. LIQUIDS and GASES do not, as they occupy the container’s shape and size.

Right answer is (d) Alkalies importance

The BEST I can EXPLAIN: Sushruta Samhita is WRITTEN by Sushruta, It’s in Sanskrit and CONTAINS text about various medicinal sciences and surgical procedures. It’s an old ancient book of India. It has great historical importance as it contains the detailed procedures and the proper instruments NEEDED.

The correct choice is (d) CH2O

For explanation I would SAY: In the molecular formula of GLUCOSE that is C6H12O6, the carbon, hydrogen, and oxygen are in the ratio of 6:12:6 RESPECTIVELY. So by simplifying them into simpler whole NUMBERS, we obtain 1:2:1. Therefore the empirical formula is CH2O.

Correct option is (d) Molecular mass

The best I can EXPLAIN: Molecular mass is the sum of ATOMIC masses of the elements present in a molecule. Gram FORMULA mass is the amount of a compound with the EXACT mass in grams as the formula mass in AMU. The standard unit of mass that measures mass on the molecular scale or an atomic scale is “amu”.

Right CHOICE is (c) A NEW System of Chemical PHILOSOPHY

The explanation is: Dalton published ” A New System of Chemical Philosophy” in 1808. He proposed a theory in that, that is Dalton’s atomic theory. It also has some limitations LIKE it couldn’t EXPLAIN how molecules combine i.e. their driving force.

The correct ANSWER is (B) 7

For explanation: There are seven scientific fundamental quantities i.e. Length(l), Time(t), Mass(m), Electric current(I), Thermodynamic temperature(T), Amount of substance(n) & Luminous intensity(Iv). They can’t be expressed as other quantities i.e. INDEPENDENT.

Correct choice is (d) 58.5 u

Explanation: As CL in NaCl can’t EXIST in the SOLID state, we can only calculate it’s formula mass. the individual mass of sodium is 23 u, whereas that of chlorine is 35.5 u. Together formula mass f Sodium CHLORIDE is the sum of individual masses, 23 + 35.5 = 58.5 u.

The correct option is (d) 4.7

For EXPLANATION I would SAY: 1.2 x 3.91 = 4.692. Since 1.2 has two significant figures, the result should not have more than two significant figures, thus, it is 4.7. As PER the rules of significant figures, the resultant answer should not have more significant figures the NUMBER with a less significant figured number.

The correct choice is (b) Heterogeneous SUBSTANCES

The BEST EXPLANATION: Heterogeneous substance is a mixture of different components non-uniformly. Homogeneous substances is a uniform mixture of substances. A PURE substance has a fixed composition. Whereas elements are composed of only ONE substance.

Right CHOICE is (b) AZT (AZIDOTHYMIDINE)

Easy explanation: The DRUG AZT is used for preventing or treating AIDS, while cisplatin & taxol are for cancer and codeine is a sort of painkiller. The drug AZT is also known as Zidovudine. This drug AZT is an antiretroviral drug. It’s used along with other drugs as a COMBINATION.

Correct choice is (a) 2moles

The explanation is: The chemical equation of water FORMATION is 2H2 + O2 → 2H2O. Though we have 8G of hydrogen, here OXYGEN is the limiting reagent. So the only 4g of hydrogen can be used to PRODUCE water i.e. 36g of water. That is 2 moles.

The correct option is (a) 6.022 x 10^22 particles

To elaborate: One MOLE of any substance contains AVOGADRO’s number of particles. Its VALUE is 6.022×10^23 atoms. But here the question is about 10 moles of a substance. So MULTIPLY the Avogadro’s number by 10. Therefore 6.022×10^23 x 10 = 6.022×10^22.

The correct choice is (b) Yes

Easiest explanation: Yes, it could explain all the LAWS of chemical combinations i.e. Law of Conservation of Mass, Law of Definite PROPORTIONS, Law of MULTIPLE Proportions, Gay Lussac’s Law of Gaseous Volumes, and AVOGADRO’s Law.

Right answer is (a) Luminous intensity

The best explanation: CANDELA is an S.I. UNIT of luminous intensity with symbol cd. It’s termed a source emitting monochromatic RADIATION at frequency 540 x 10^12 HERTZ with the radiant intensity of 1/683 watt per steradian provided in the same direction.

The correct answer is (a) 0.2143

To elaborate: Mole FRACTION of a SUBSTANCE is given by the formula: Mole fraction = No. of MOLES of that substances/No. of total moles of solution. Mole fraction of oxygen here = 3/4 + 3 + 7 = 3/14 = 0.2143.

The correct option is (d) 0.5 mol/KG

The BEST explanation: Molality of a solution is given y the FORMULA; molality = NUMBER of moles of the solute/mass of the solution. So here the number of moles is 8 and the mass of the solution is 4 kg. Molality is 8/4 = 0.5 mol/kg.

Correct answer is (b) 1.3 mol/L

For explanation: When two SOLUTIONS are combined, the resultant MOLARITY is M1V1 + M2V2/V1 + V2. Consider M1 = 1.3, M2 = 0.8, V1 = 100ml and V2 = 500ml. Now resultant molarity = 1.3(100) + 0.8(500)/100 + 500 = 0.88 mol/L.

Correct option is (C) 14

For explanation I would SAY: Given that, carbon-12 is of 70% and carbon-14 is of 30%. In order to find AVG atomic mass, you should add the products of multiplications 12 with 70/100 and 14 with 30/100. 12 x 0. 7 = 9.8; 14 x 0.3 = 4.2. Now adding them 9.8 + 4.2 = 14.

The CORRECT answer is (a) reason for combining atoms

Easiest explanation: Dalton’s ATOMIC theory couldn’t explain the reason for combining atoms. This is one of the major limitations of Dalton’s atomic theory. THOUGH it could explain the conservation of MASS, indivisible atoms and definite PROPORTIONS.

Correct choice is (b) accurate

Easiest explanation: These values are accurate as they are nearer to the exact VALUE. Precision is REFERRED to as the closeness of different measurements for the same QUANTITY. Accuracy is the DEGREE to which it’s taken as standard or almost equivalent to it.

The CORRECT answer is (a) 12.7 cm

Easiest EXPLANATION: 1 inch = 2.54 cm : 1 cm = 0.3931 inch. As we now know, how much is 1inch in centimeters, then we need to MULTIPLY 5 to 2.54 cm in order to CONVERT it into centimeters. 5 x 2.54 cm = 12.7 cm.

Correct answer is (c) 3

Easiest EXPLANATION: The non-zero digits and any zeros between them are all significant. LEADING zeros are not significant. COUNTING all the significant digits gives us 3.

Correct answer is (c) 1:2:1

Easiest explanation: the molecular formula of glucose is C6H12O6. The RATIO in the molecular formula is 6:12:6; carbon, HYDROGEN, and oxygen RESPECTIVELY. So by simplifying them into SIMPLER whole numbers, we obtain 1:2:1.

Correct answer is (b) H2O2

The explanation: The MOLECULAR formula is the exact number of different types of atoms present in the molecule of a COMPOUND. The rest COMPOUNDS are not in the same ratio as of EMPIRICAL formula ones. Though HO is possible, it can’t exist.

Right answer is (a) C2H5OH

The explanation: As per the above question, the compounds consist of carbon, HYDROGEN, and oxygen in the ratio of 52.17:13.04:34.78 respectively. Now multiply the ratio with the MOLECULAR mass that is 46 g. HENCE we obtain it as 2400:600:1600 that is 24:6:16 (2 atoms of carbon + 6 atom of hydrogen + 1 atom of oxygen). The required compound is C2H5OH.

The correct option is (c) Atomic mass UNIT

Best explanation: The Atomic mass unit is a standard unit of mass that measures mass on an atomic or molecular SCALE. One unit of it is practically equal to 1.66056×10^-24 G. 1 amu is defined as a mass that is almost equal to one-twelfth of the mass of one carbon – 12 atom.

Correct option is (B) False

To explain: Compounds cannot be SEPARATED simply by physical methods, but they need chemical methods because when its components are mixed they CHANGE their chemical formulae and combine with each other to FORM a NEW chemical formula, resulting in a compound.

The CORRECT option is (B) C5H10

For explanation: C5H10 cannot be an empirical formula because of the CARBON and hydrogen RATIO in this compound is5:10 respectively. They are not in the simplest possible WHOLE numbered ratio (1:2 is the simplest for this compound). Hence it cannot be an empirical compound.

The correct OPTION is (C) 44

To EXPLAIN: The individual mass of carbon is 12 amu and the individual mass of OXYGEN is 16 amu. The formula for carbon dioxide is CO2. Thus one carbon and two OXYGENS. 12(carbon M.wt) + 2 x 16(oxygen M.wts) = 12 + 32 = 44. Therefore the molecular mass of carbon dioxide is 44.

Right answer is (b) Atoms

To explain I would say: ATOM is the basic unit of life. A molecule is a compound made up of 2 or more atoms HELD by CHEMICAL bonds. The mixture is a COMBINATION of pure substances in a ratio. Ion is either positively or negatively charged.

Right answer is (a) 2

To explain I would SAY: The non-zero digits and any zeros between them are all SIGNIFICANT. Leading zeros are not significant. COUNTING all the significant digits GIVES us 2.

The correct choice is (a) 6.354 x 10^9

The best I can EXPLAIN: Scientific notation should have the LEAST possible significant figures as the zeroes are made as to the power of ten. Or simply the power of ten in scientific notation is EQUAL to the number of times the decimal POINT moved to produce a number between 1 and 10.

Right answer is (a) Molecular

Easiest explanation: The molecular formula is the exact NUMBER of different TYPES of atoms present in the molecule of a compound. An empirical formula is the simplest whole number ratio of VARIOUS atoms present in a compound. Therefore we can CALCULATE the molecular formula if the molar mass is KNOWN.

The correct ANSWER is (b) 2.1g

For explanation I would say: Given that, 1 mole of ammonia is of 17 g. 0.3 mole of ammonia contains 17 X 0.3g of mass. IT’s because the MOLECULAR WEIGHT of a given pcompound is directly proportional to the number of moles of the given compound.

The correct choice is (a) u

To explain I WOULD SAY: Presently, “amu” has been replaced by “u”. Atomic MASS unit is “amu”, but now as it has been changed to “u”, & now known as unified mass. One unified atomic mass unit is the mass of one nucleon and is also equal to 1 g/mol.

Correct ANSWER is (a) True

The best I can EXPLAIN: In the above given equation 1 u = Mu/NA; “u” refers to the atomic mass UNIT, Mu refers to molar mass constant(Its value is DEFINED to be 1 g/mol in SI units). 1 u = Ma/NA = 1.660539040 x 10^-27 kg. Hence the above statement is true.

Right option is (d) 1.0080 AMU

Explanation: The mass of a hydrogen atom is 1.6736×10^-24 G. When converted in terms of amu, 1.6736×10^-24 g should be divided by 1.66056×10^-24 g. 1.6736×10^-24 g/1.66056×10^-24 g = 1.0078 amu = 1.008 amu. This the PROCESS to MEASURE any atomic mass in amu.

Right option is (b) False

Easy explanation: Law of conservation of mass is EXPLAINED in Dalton’s atomic theory. He said that reorganization of atoms is INVOLVED in chemical REACTIONS. This MEANS mass is neither created nor DESTROYED in a chemical reaction i.e. explained.

Right option is (b) MASS can NEITHER be created nor destroyed is Law of Conservation of Volume

Easy explanation: The CORRECT statement is mass can neither be created nor destroyed is the Law of Conservation of Mass. On conducting many experiments regarding COMBUSTION and noticing various physical and CHEMICAL changes, there is no change in overall mass hence conservation of mass.

Correct option is (C) LAW of Definite Proportion

Easiest explanation: JOSEPH Proust worked about the composition of elements present in a compound experimentally, he concluded that from any source, a particular compound ALWAYS CONTAINS the same elements in the same proportion by mass/weight. Hence it can also be known as the Law of Definite Proportion.

Right CHOICE is (c) 104°F

The BEST I can EXPLAIN: 1 Fahrenheit = 9/5 Centigrade + 32.

9(40)/5 + 32 = 9 x 8 + 32 = 104°F.