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Question
What are the common physical features of alkali metals?
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Solution
Physical properties of alkali metals are as follows.
- They are quite soft and can be cut easily. Sodium metal can be easily cut using a knife.
- They are light coloured and are mostly silvery-white in appearance.
- They have low density because of their large atomic sizes. The density increases down the group from Li to Cs. The only exception to this is K, which has a lower density than Na.
- The metallic bonding present in alkali metals is quite weak. Therefore, they have low melting and boiling points.
- Alkali metals and their salts impart a characteristic colour to flames. This is because the heat from the flame excites the electron present in the outermost orbital to a high energy level. When this excited electron reverts back to the ground state, it emits excess energy as radiation that falls in the visible region.
- They also display a photoelectric effects. When metals such as Cs and K are irradiated with light, they lose electrons.
RELATED QUESTIONS
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(ii) MgSO4
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Match List-I with List-II.
| List-I | List-II |
| (Metal) | (Application) |
| (a) Cs | (I) High temperature thermometer |
| (b) Ga | (II) Water repellent sprays |
| (c) B | (III) Photoelectric cells |
| (d) Si | (IV) Bullet proof vest |
Choose the most appropriate answer from the options given below:
A white precipitate was formed when BaCl2 was added to extract of an inorganic salt. Farther, a gas 'X' with characteristic odour was released when the formed white precipitate was dissolved in dilute HCl. The anion present in the inorganic salt is ______.
The metal mainly used in devising photoelectric cells is ______.
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Nitrogen combines with metals to form ______.
Given below are two statements, one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : Lithium salts are hydrated.
Reason (R) : Lithium has higher polarising power than other alkali metal group members.
In the light of the above statements, choose the most appropriate answer from the options given below :
KO2 (potassium super oxide) is used in oxygen cylinders in space and submarines because it ______.
Which element from following is used as moderator in nuclear reactor?
