- A. Copper
- B. Mercury
- C. Silver
- D. Gold
(b) Mercury
- A. Plutonium
- B. Neptunium
- C. Uranium
- D. Mercury
(d) Mercury
- A. Ag
- B. Hg
- C. Au
- D. Pb
(b) Hg
- A. Nitrogen
- B. Oxygen
- C. Chlorine
- D. Carbon
(d) Carbon
- A. Ductility
- B. Malleability
- C. Conductivity
- D. Tensile strength
(b) Malleability
- A. Carbon
- B. Oxygen
- C. Aluminium
- D. Sulphur
(a) Carbon
8th Science Matter Around Us Book Back Answers Question 10
Pencil lead contains –
(a) Graphite
(b) Diamond
(c) Aluminium
(d) Sulphur
(a) Graphite
Metalloids
W
Higher
Hydrogen, oxygen
Silicon / Germanium
False.
Correct statement:
Metals are generally good conductors of heat and electricity.
False.
Correct statement:
Gallium (Ga) become liquid at or just above room temperature.
- (a) For making wires 2. Copper
- (b) Sewing needle 3. Tungsten
- (c) As a fuel for ignition in rocket. 4. Boron
- (d) Making the filament of a bulb
B
A
D
C
- A. 1 – A, 2 – C, 3 – B, 4 – D
- B. 1 – C,2 – A, 3 – B, 4 – D
- C. 1 – D, 2 – C, 3 – B, 4 – A
- D. 1 – B, 2 – C, 3 – A, 4 – D
A
C
B
D
Compound
Symbols
Constituent elements
Carbon monoxide
(CO)
Carbon and oxygen
Washing soda
(Na 2 CO 3 )
Sodium, carbon and oxygen
S.No
Element
Symbols
(i)
Oxygen
O
(ii)
Gold
Au
(iii)
Calcium
Ca
(iv)
Cadmium
Cd
(v)
Iron
Fe
Oxygen is essential for our life and all living beings inhale it during breathing.
On being hit, metals produce a typical sound. They are said to be sonorous. This property is being made used in making bells.
A chemical symbol is a shorthand method of representing an element.
Symbol of an element signifies:
Name of the element.
One atom of the element for example,
The symbol O stands for the element of oxygen.
One atom of oxygen.
Boron and silicon.
Water
Hydro chloric Acid
Nitric Acid
Properties of metalloids:
Metalloids are all solid at room temperature.
They can form alloys with other metals
Some metalloids, such as silicon and germanium, can act as electrical conductors under the specific conditions, thus they are called semiconductors.
Silicon for example appears lustrous, but is not malleable nor ductile (it is brittle – a characteristic of some non – metals). It is a much poorer conductor of heat and electricity than the metals
No, we cannot store the lemon pickle in aluminium utensil because aluminium is a metal and lemon is acidic. The acids react with metals to give hydrogen which would spoil the food and makes it unfit to use.
The cooking utensils are made up of aluminium and brass because they are good conductors of heat.
Aluminium will form a layer of protective oxide that prevents further reaction. Also aluminium is also relatively cheap and that is why it is used widely in making utensils.
Alchemy was form of chemistry studied in the middle age, which was concerned with trying to discover ways to change ordinary metals into gold.
Na – Sodium
W – Tungsten
Ba – Barium
Al – Aluminium
U – Uranium.
S.No
Non – metals
Symbols
1.
Sulphur
S
2.
Carbon
c
3.
Oxygen
0
4.
Hydrogen
H
5.
Helium
He
6.
Nitrogen
N
Silver and gold are used for making jewels and in decorative purposes
S.No
Compounds
Uses
(i)
Baking soda
Fire extinguisher, preparation of baking powder and preparation of cakes and bread.
(ii)
Bleaching powder
As bleaching agent, disinfectant and sterilisation of drinking water.
(iii)
Quick lime
Manufacture of cement and glass.
Wires cannot be drawn from materials such as stone or wood, is because these materials are non – conductors of electricity.