Choose the correct answer :
[question] Question. Choose the correct answer : Isotopes of an element have (a) The same physical properties (b) Different chemical properties (c) Different number of neutrons (d) Different atomic numbers [/question] [solution] Solution: (c) [/solution]...
Read More →Which of the following statements is not a correct
[question] Question. Which of the following statements is not a correct statement about the trends when going from left to right across the periods of Modern Periodic Table. (a) The elements become less metallic in nature. (b) The number of valence electrons increases. (c) The atoms lose their electrons more easily (d) The oxides become more acidic. [/question] [solution] solution: (c) The atoms lose their electrons more easily. [/solution]...
Read More →Choose the correct answer :
[question] Question. Choose the correct answer : Rutherford’s alpha-particle scattering experiment was responsible for the discovery of (a) Atomic nucleus (b) Electron (c) Proton (d) Neutron [/question] [solution] Solution: (a) [/solution]...
Read More →Give examples of polynomials p(x),
[question] Question. Give examples of polynomials p(x), g(x),q(x) and r(x), which satisfy the division algorithm and (i) deg p(x) = deg q(x) (ii) deg q(x) = deg r(x) (iii) deg r(x) = 0. [/question] [solution] Solution: (i) $p(x)=2 x^{2}+2 x+8, g(x)=2 x^{0}=2$ $q(x)=x^{2}+x+4 ; r(x)=0$ (ii) $\mathrm{p}(\mathrm{x})=2 \mathrm{x}^{2}+2 \mathrm{x}+8 ; \mathrm{g}(\mathrm{x})=\mathrm{x}^{2}+\mathrm{x}+9$; $q(x)=2 ; r(x)=-10$ (iii) $\mathrm{p}(\mathrm{x})=\mathrm{x}^{3}+\mathrm{x}+5 ; \mathrm{g}(\mathrm...
Read More →By considering their position in the Modern Periodic Table,
[question] Question. By considering their position in the Modern Periodic Table, which one of the following elements would you expect to have maximum metallic characteristic? Ga, Ge, As, Se, Be [/question] [solution] solution: Galium (Ga). [/solution]...
Read More →For the following statements,
[question] Question. For the following statements, write T for ‘True’ and F for ‘False’. (a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons. (b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral. (c) The mass of an electron is about $\frac{1}{2000}$ times that of proton. (d) An isotope of iodine is used for making tincture iodine, which is used as a medicine. [/question] [solution] Solution: (a) (F) (b) (F) (c) (T) (d) (F) [/so...
Read More →In the Modern Periodic Table,
[question] Question. In the Modern Periodic Table, which are the metals among the first ten elements? [/question] [solution] solution: Among the first ten elements, lithium (Li) and beryllium (Be) are metals. [/solution]...
Read More →Composition of the nuclei of two atomic
[question] Question. Composition of the nuclei of two atomic species X and Y are given as under Give the mass numbers of X and Y. What is the relation between the two species? [question] [solution] Solution: Mass number of X = Number of protons + Number of neutrons = 6 + 6 = 12 Mass number of Y = Number of protons + Number of neutrons = 6 + 8 = 14 These two atomic species X and Y have the same atomic number, but different mass numbers. Hence, they are isotopes. [/solution]...
Read More →(a) Lithium, sodium,
[question] Question. (a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements? (b) Helium is an non-reactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common? [/question] [solution] solution: (a) Yes. The atoms of all the three elements lithium, sodium, and potassium have one electron in their outermost shell. (b) Both helium (He) and neon (Ne) have fille...
Read More →On dividing $x^{3}-3 x^{2}+x+2$ by a polynomial $g(x)$
[question] Question. On dividing $x^{3}-3 x^{2}+x+2$ by a polynomial $g(x)$, the quotient and remainder were $x$ $-2$ and $-2 x+4$, respectively. Find $g(x)$ [/question] [solution] Solution: $\left(x^{3}-3 x^{2}+x+2\right)=g(x) \times(x-2)+(-2 x+4)$ $\Rightarrow x^{3}-3 x^{2}+x+2+2 x+-4=g(x) \times(x-2)$ $\Rightarrow x^{3}-3 x^{2}+3 x-2=g(x) \times(x-2)$ $g(x)=\frac{x^{3}-3 x^{2}+3 x-2}{x-2}$ So, $g(x)=x^{2}-x+1$ [/solution]...
Read More →Name
[question] Question. Name (a) three elements that have a single electron in their outermost shells. (b) two elements that have two electrons in their outermost shells. (c) three elements with filled outermost shells. [/question] [solution] solution: (a) Lithium (Li), sodium (Na), and potassium (K) have a single electron in their outermost shells. (b) Magnesium (Mg) and calcium (Ca) have two electrons in their outermost shells. (c) Neon (Ne), argon (Ar), and xenon (Xe) have filled outermost shell...
Read More →If Z = 3, what would be the valency of the element?
[question] Question. If Z = 3, what would be the valency of the element? Also, name the element. [/question] [solution] Solution: By Z = 3, we mean that the atomic number of the element is 3. Its electronic configuration is 2, 1. Hence, the valency of the element is 1 (since the outermost shell has only one electron). Therefore, the element with Z = 3 is lithium. [/solution]...
Read More →Obtain all other zeros of $3 x^{4}+6 x^{3}-2 x^{2}-10 x-5$
[question] Question. Obtain all other zeros of $3 x^{4}+6 x^{3}-2 x^{2}-10 x-5$, if two of its zeros are $\sqrt{\frac{5}{3}}$ and $-\sqrt{\frac{5}{3}}$ [/question] [solution] Solution: Two of the zeros of $3 x^{4}+6 x^{3}-2 x^{2}-10 x-5$ are $\sqrt{\frac{5}{3}}$ and $-\sqrt{\frac{5}{3}}$. $\Rightarrow\left(x-\sqrt{\frac{5}{3}}\right)\left(x+\sqrt{\frac{5}{3}}\right)$ is a factor of the polynomial. i.e., $\mathrm{x}^{2}-\frac{\mathbf{5}}{\mathbf{3}}$ is a factor. i.e., $\left(3 x^{2}-5\right)$ is...
Read More →Name two elements you would expect to show chemical reactions similar to magnesium.
[question] Question. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice? [/question] [solution] solution: Calcium (Ca) and Strontium (Sr) are expected to show chemical reactions similar to nagnesium $(\mathrm{Mg})$. This is because the number of valence electrons $(2)$ is same in all these hree elements. And since chemical properties are due to valence electrons, they show same hemical reactions. [/solution]...
Read More →The average atomic mass of a sample of an element X is
[question] Question. The average atomic mass of a sample of an element $X$ is $16.2 \mathrm{u}$. What are the percentages of isotopes ${ }_{8}^{16} \mathrm{X}$ and ${ }_{8}^{18} \mathrm{X}$ in the sample? [/question] [solution] Solution: Suppose percentage of isotope ${ }_{8}^{16} \mathrm{X}=\mathrm{x}$ Then percentage of isotope ${ }_{8}^{18} \mathrm{X}=(100-\mathrm{x})$ $\therefore$ Average atomic mass $=\frac{16 \times x+18(100-x)}{100}$ $=\frac{1800-2 x}{100}=18-0.02 x$ $\therefore 18-0.02 \...
Read More →How could the Modern Periodic Table remove
[question] Question. How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table? [/question] [solution] solution: Modern periodic table is based on atomic numbers whereas Mendeleev’s periodic table was based on atomic masses. So, properties of elements could be explained with more precision when elements were arranged on the basis of increasing atomic number. For example : (i) The position of isotopes is taken care of when the elements are arranged in the ascendin...
Read More →Read the following statements about a constitution.
[question] Question. Read the following statements about a constitution. Give reasons why each of these is true or not true. (a) The authority of the rules of the constitution is the same as that of any other law. (b) Constitution lays down how different organs of the government will be formed. (c) Rights of citizens and limits on the power of the government are laid down in the constitution. (d) A constitution is about institutions, not about values. [/question] [solution] Solution: (a) True Th...
Read More →Check whether the first polynomial is a factor of the second polynomial
[question] Question. Check whether the first polynomial is a factor of the second polynomial by dividing the second polynomial by the first polynomial. (i) $t^{2}-3,2 t^{4}+3 t^{3}-2 t^{2}-9 t-12$ (ii) $x^{2}+3 x+1,3 x^{4}+5 x^{3}-7 x^{2}+2 x+2$ (iii) $x^{3}-3 x+1, x^{5}-4 x^{3}+x^{2}+3 x+1$ [/question] [solution] Solution: Hence, $t^{2}-3$ is a factor of $2 t^{4}+3 t^{3}-2 t^{2}-9 t-12$ (ii) $x^{2}+3 x+1$ Hence, $x^{2}+3 x+1$ is a factor of $3 x^{4}+5 x^{3}-7 x^{2}+2 x+2$ (iii) $x^{3}-3 x+1$ He...
Read More →The average atomic mass of a sample of an element
[question] Question. The average atomic mass of a sample of an element $\mathrm{X}$ is $16.2 \mathrm{u}$. What are the percentages of isotopes ${ }_{8}^{16} \mathrm{X}$ and ${ }_{8}^{18} \mathrm{X}$ in the sample? [/question] [solution] Solution: Suppose percentage of isotope ${ }_{8}^{16} \mathrm{X}=\mathrm{x}$ Then percentage of isotope ${ }_{8}^{18} \mathrm{X}=(100-\mathrm{x})$ $\therefore$ Average atomic mass $=\frac{16 \times x+18(100-x)}{100}$ $=\frac{1800-2 x}{100}=18-0.02 x$ $\therefore ...
Read More →Why do you think the noble gases
[question] Question. Why do you think the noble gases are placed in a separate group ? [/question] [solution] solution: Noble gases are inert elements and thus, they do not form compounds. Their properties are different from all the other elements. Therefore, the noble gases are placed in a separate group. [/solution]...
Read More →Here are different opinions about what made India a democracy.
[question] Question. Here are different opinions about what made India a democracy. How much importance would you give to each of these factors? (a) Democracy in India is a gift of the British rulers. We received training to work with representative legislative institutions under the British rule. (b) Freedom struggle challenged the colonial exploitation and denial of different freedoms to Indians. Free India could not be anything but democratic. (c) We are lucky to have leaders who had democrat...
Read More →What were the criteria used by
[question] Question. What were the criteria used by Mendeleev in creating his Periodic Table ? [/question] [solution] solution: Mendeleev’s periodic table was based on the observation that the properties of elements are a periodic function of their atomic masses. This means that if elements are arranged in the increasing order of their atomic masses, then their properties get repeated after regular intervals. [/solution]...
Read More →Besides gallium,
[question] Question. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his periodic table (any two) ? [/question] [solution] solution: Scandium and germanium. [/solution]...
Read More →If bromine atom is available in the form
[question] Question. If bromine atom is available in the form of $\mathrm{Br}^{79}, \mathrm{Br}^{81}$, say, two isotopes $(49.7 \%)$ and $(50.3 \%)$, calculate the average atomic mass of bromine atom. [/question] [solution] Solution: It is given that two isotopes of bromine are $(49.7 \%)$ and $(50.3 \%) .$ Then, the average atomic mass of bromine atom is given by : $\therefore$ Average atomic mass of Br $=\frac{49.7 \times 79+50.3 \times 81}{100}=\frac{3926.3+4074.3}{100}$ $=39.263+40.743=80.00...
Read More →Here are some of the guiding values of the Constitution and their meaning.
[question] Question. Here are some of the guiding values of the Constitution and their meaning. Rewrite them by matching them correctly. [/question] [solution] Solution: [/solution]...
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