A. The elements Li, Na, and K, each having one valence electron, are in period 2, 3 and 4 respectively of modern periodic table.

(i) To which group of the modern periodic table these elements belong? [1 mark]
(ii)Which one of them is least reactive? [1 mark]
(iii) Which one of them has the largest atomic radius? [1 mark]

B. What is a chemical symbol of an element? What information does it convey? [3 marks]

C. (i) During photosynthesis, plants use light energy to prepare food. How will you classify the photosynthesis process based on the release/absorption of energy? [1 mark]

(ii) Write the chemical reaction where the following changes are observed. [3 marks]
(a) Gas is evolved

(b) Colour change is noticed

(c) Precipitate is formed

(d) Physical state is changed

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Solution

A.(i)The given elements belong to Group 1 of the modern periodic table as all of them have one valence electron. [1 mark]
(ii) Li is least reactive because its outermost orbit is very near to the nucleus. So the removal of electron is difficult. [1 mark]
(iii) K has the largest atomic radius because it has more number of shells as compared to Na and Li. [1 mark]

B.
(i) A chemical symbol is the short form which stands for an atom of a specific element or the abbreviations used for the names of elements. [1 mark]
(ii) It represents a specific element. [0.5 mark]
(iii) It represents one atom of an element. [0.5 mark]
(iv) A symbol represents how many atoms are present in one gram (gm) atom. [0.5 mark]
(v) The chemical symbol of an element represents the mass of an atom of that element. [0.5 mark]

C. (i) During photosynthesis, the energy in the form of sunlight (a form of energy) is absorbed by the green plants in order to prepare their food.
Such a type of reaction in which energy is absorbed is called an endothermic reaction. [1 mark]

(ii) (a) Reaction between baking soda and vinegar. Baking soda on reaction with vinegar produces carbon dioxide.
The chemical equation for the overall reaction is:

$N a H C O_{3 (s)}$ + $C H_{3} C O O H_{(l)}$ $\to$ $C O_{2 (g)}$ + $H_{2} O_{(l)}$ + $N a_{(a q)}^{+}$ + $C H_{3} C O O^{-} (a q)$

with s = solid, l = liquid, g = gas, aq = aqueous or in water solution

Another common way to write this reaction is:

$N a H C O_{3}$ + $H C_{2} H_{3} O_{2}$ $\to$ $N a C_{2} H_{3} O_{2}$ + $H_{2} O$ + $C O_{2}$ [1 mark]

(b) Change in colour: Reaction between lead nitrate solution and potassium iodide solution.

$P b (N O_{3})_{2 (a q)}$ + $2 K l$ $\to$ $P b l_{2 (s)}$ + $2 K N O_{3 (a q)}$

In this reaction, colour changes from colourless to yellow.
[0.5 mark]
(c) Formation of precipitate: Action of barium chloride on sodium sulphate.

$B a C l_{2 (a q)}$ + $N a_{2} S O_{4 (a q)}$ $\to$ $B a S O_{4 (s)}$ + $2 N a C l_{(a q)}$

$B a S O_{4 (s)}$ - ppt
[0.5 mark]
(d) Physical state

Change in temperature: Action of dilute sulphuric acid on zinc.

$Z n_{(s)}$ + $H_{2} S O_{4 (a q)}$ $\to$ $Z n S O_{4 (a q)}$ + $H_{2}$

In this reaction, heat is evolved. [1 mark]

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Similar questions

Na, Mg, and Al are the elements of the 3rd period of the Modern Periodic Table having group numbers 1, 2, and 3 respectively. Which one of these elements has the highest valency (b) largest atomic radius and (c) maximum chemical reactivity? Justify your answer stating the reason for each.

Q. (a) What were the two major shortcomings of Mendeleev's periodic table? How have these been removed in the modern periodic table?
(b) Two elements X and Y have atomic numbers 12 and 16 respectively. Write the electronic configuration for these elements. To which period of the modern periodic table do these two elements belong? What type of bond will be formed between them and why?
(c) To which groups of the modern periodic table do the elements X and Y belong? Give reason for your answer.
(d) What could the elements X and Y be? Write their names and symbols.

Q. (a) Explain why, the first period of the modern periodic table has only two elements whereas second period has eight elements
(b) Why do elements in the same group show similar properties but the elements in different groups show different properties?
(c) For each of the following triads, name the element with the characteristics specified below:

Elements	Least atomic radius	Chemically least reactive
(i) F, Cl, Br (ii) Li, Na, K	.................... ....................	.................... ....................

(d) State one reason for keeping fluorine and chlorine in the same group of the periodic table.
(e) What are the merits of the modern periodic table of elements?

Q. A. The elements Li, Na, and K, each having one valence electron, are in period 2, 3 and 4 respectively of modern periodic table.

(i) To which group of the modern periodic table these elements belong? [1 mark]
(ii)Which one of them is least reactive? [1 mark]
(iii) Which one of them has the largest atomic radius? [1 mark]

B. What is a chemical symbol of an element? What information does it convey? [3 marks]

C. (i) Explain the effect of temperature on solubility of solid solutes. [1 mark]
(ii) A student wants to prepare a solution of acetone and water having

30 %

v/v. If

6 m L

of acetone has been taken then how much water must be added to get the desired concentration? [3 marks]

Q. The elements Li, Na, and K, each having one valence electron, are in period 2, 3 and 4 respectively of modern periodic table.

i. To which group of the modern periodic table these elements belong?

ii. Which one of them is least reactive?

iii. Which one of them has the largest atomic radius?

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