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प्रश्न
The atomic masses of three elements A, B and C having similar chemical properties are 7, 23 and 39, respectively.
- Calculate the average atomic mass of elements A and C.
- Compare the average atomic mass with atomic mass of B.
- What could the elements A, B and C be?
उत्तर
(a) The average atomic mass of elements A and C = `(7+39)/2=46/2=23`
(b) The average atomic mass of elements A and C is equal to the atomic mass of element B.
(c) A is lithium, B is sodium and C is potassium.
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संबंधित प्रश्न
Name any two elements of group one and write their electronic configurations. What similarity do you observe in their electronic configurations? Write the formula of oxide of any of the aforesaid elements.
How many groups and periods are there in the modern periodic table?
How do the atomic size and metallic character of elements vary as we move :-
(a) down a group and
(b) from left to right in a period
In the following set of element, one element does not belong to the set. Select this element and state why it does not belong:
Calcium, Magnesium, Sodium, Beryllium
How does the tendency to gain electrons change as we go down in group 17 of the periodic table? Why does it change this way?
Five elements A, B, C, D and E have atomic numbers of 2, 3, 7, 10 and 18 respectively. The elements which belong to the same period of the periodic table are:
(a) A, B, C
(b) B, C, D
(c) A, D, E
(d) B, D, E
The elements A, B, C, D and E have atomic numbers 9, 11, 17, 12 and 13 respectively. The pair of elements which belongs to the same group of the periodic table is:
(a) A and B
(b) B and D
(c) A and C
(d) D and E
Given alongside is a part of the periodic table. As we move vertically downward from Li to Fr:
| Li | Be |
| Na | |
| K | |
| Rb | |
| Cs | |
| Fr | Ra |
What happens to their metallic character?
Where would you locate the element with electronic configuration 2, 8 in the modern periodic table?
An element has 2 electrons in its N shell.
State the name assigned to this group.
State the valency of the elements of periods 3 and write the formula of their oxides.
How does the number of:
valence electrons and
An element barium has atomic number 56. Look up its position in the periodic table and answer the following question.
Is it more or less reactive than calcium?
An element X belong to 3rd periods and group II of the periodic table state:
the valency,
Name the element which has the electronic configuration 2, 8, 3?
What is the common feature of the electronic configuration of the elements at the end of period 2, and period 3?
Write two reasons responsible for late discovery of noble gases ?
F, Cl and Br are the elements each having seven valence electrons. Which of these (i) has the largest atomic radius, (ii) is most reactive? Justify your answer stating reason for each.
Atomic number of metal ‚A‛ is 11, while atomic number of metal ‚B‛ is 20. Which of them will be more reactive? Write the chemical reaction of dilute HCl with metal ‚A‛.
What is modern periodic law?
State whether the following statement is true or false
Similar electronic configuration is repeated after intervals of 2, 8, 8, 18 and 32.
State the number of elements in period 1, period 2 and period 3 of the periodic table.
Copy and complete the following sentence choosing the correct word or words from those given below, at the end of the sentence:
The similarities in the properties of elements belonging to a group are because they have the same ______
Atomic number of an element is 16. State
- the period to which it belongs
- the number of valence electrons
- whether it is a metal or non-metal
In the above table, H does not represent hydrogen.Some elements are given in their own symbol and position in the periodic table while others are shown with a letter. With refrence to the table answer the following questions.
1. Identify the most electronegative element.
2. Identify the most reactive element of Group I.
3. Identify the element from Period 3 with least atomic size.
4. How many valence electrons are present in Q?
5. Which element from group 2 would have the least ionisation energy?
6. Identify the noble gas of the fourth period.
7. In the compound between A and H, what type of bond would be formed and give its molecular formula.
Choose the correct answer from the choice given:
An element A belonging to Period 3 and Group II will have
Arrange the following as per instruction given in the bracket
Na, K, Cl, S, Si (increasing ionisation potential)
Arrange the following in order of increasing radii:
Mg2+, Mg, Mg+
With reference to the variation of properties in the Periodic table, which of the following is generally true?
Formula of ion of A is A2+. Element A probably belongs to ______ group.
Moving left to right in the second period, the number of valence electrons _____.
Moving down in the second group, number of valence electrons ______.
An element A has 2 electrons in its fourth shell. State:
its valency
Based on the group valency of element write the molecular formula of the following compound giving justification:
Oxide of first group elements.
What is the common feature of the electronic configuration of the elements at the end of Period 2 and Period 3?
Name or state following with reference to the element of the first three periods of the periodic table.
A non-metal in period 2 having electronic configuration 2, 6.
Match the option A and B with the statements (i) and (ii):
| A. metal | (i) The metal that forms two types of ion. |
| B. iron | (ii) An element with electronic configuration 2, 8, 8, 3. |
