1. Why do we wrap a blanket around a person whose clothes have caught fire?
2. Why curd set faster in summer than in winter?
3. Why are the handles of pressure cooker made up of plastic? Name the type of the plastic.
4. Why is it necessary to conserve forest?
5. Why zinc can displace copper from copper sulphate solution?
6. Why methane and LPG are considered as ecofriendly fuel?
7. Why Aluminum is not used to make electrical wire when it is cheaper and lighter than silver?
8. Why drip irrigation considered as best method of irrigation?
9. Why is white phosphorous is stored under water?
10. Why hydrogen is used as rocket fuel?
Q4) Read the passage and answer the following question:
Some microorganisms are useful to us in many ways. A bacterium called Lactobacillus is useful in making curd
from milk. Milk contain lactose, curd contains the bacterium Lactobacillus that helps to convert lactose in the milk
to lactic acid. In this way curd is formed from milk.
Answers
Answer
1) As the fire blanket completely
surrounds the person whose clothes
caught fire, it seals the person's body
surface around the fire and cut's off
the oxygen supply to the fire, thereby
putting it out.
2). This is because in summers, the bacterium responsible for turning milk into curd,
Lactobacillus, gets an optimum temperature for growth and thus multiplies faster
3). Pressure cooker handles are made up
Bakelite. Bakelite is used because it has
hear-resistant properties and is an electrical
insulator. Hence, Pressure c0oker handles are
made up of plastic.
4). We should conserve forests and wildlife
because they are essential for us in the
following terms: Forest provide us with
oxygen, they cause rainfall. Forest prevents
soil erosion. Plants are dependent on animals
and birds for their pollination and seed
dispersal.
5). Zinc (Zn) metal is more reactive than copper
(Cu) so it displaces copper from copper
sulphate (CuSO,) solution forming zinc
sulphate (ZnSO,) and copper. This type of
reaction is called a displacement reaction.
CuSO(ag) + Zn(s) ZnSO,(aq)+ Cu(s)
6).(i) It has high calorific value.
(it) Easily transportable.
(iii) Does not produce any smoke on
burning.
(iu) No residue left after burning.
7). Aluminium is used in making electrical
wires as it is light, cheap and more
conductive than copper.
its True
8).The drip method of irrigation is the
best among all modern methods of
irrigation.
Because it prevents the loss of water
through evaporation and directly
reaches the ground.
10).Propellant is the chemical mixture burned to produce thrust in
rockets and consists of a fuel and an oxidizer. A fuel is a substance
that burns when combined with oxygen producing gas for
propulsion. An oxidizer is an agent that releases oxygen for
combination with a fuel. The ratio of oxidizer to fuel is called the
mixture ratio.
Propellants are classified according to their state - liquid, solid, or
hybrid. The gauge for rating the efficiency of rocket propellants
is specific impulse, stated in seconds.
Actually, initially liquid hydrogen and liquid oxygen is used. The
liquid hydrogen reacts, very violently, with oxygen and the reaction
becomes exothermic which results in lots of thrust and release of
water which further acts as cooling agent.
But, due to less availability of liquid hydrogen now hydrogen gas is
used. Its exhaust velocity is maximum in all the chemicals and so it
has been chosen and used in preference to other fuels.