The Substance which is used for making different shapes is Plaster of Paris.  Its chemical name is calcium sulphate hemihydrate \([CaSO_4.1/2H_2O].\) The two formula unit of \(CaSO_4\) share one molecule of water.  As a result, it is soft.  When it is left open for some time, it absorbs moisture from the atmosphere and forms gypsum, which is a hard solid mass.

\(\underset{Plaster\ of\ Paris}{​​CaSO_4.{1\over 2}H_2O}+1{1\over2}{H_2O}\rightarrow \underset{Gypsum}{CaSO_4.2H_2O}\)

Importance of Fuse: The electric fuse is an important device in household wiring and also in many electrical appliances. By melting, the fuse wire breaks the circuit and thus helps in saving the wiring or the appliance from damage. A fuse wire works because of its lower melting point which is possible because of its respective rating. If a fuse with larger rating is used with an appliance, the fuse wire shall not melt and hence would fail to serve the required purpose. Due to this, a fuse with defined rating should not be replaced by one with a larger rating.

(a) Yes.
(b) Geographical isolation prevents gene flow between populations of a species whereas asexual reproduction generally involves only one individual. Slowly the separated individuals will reproduce among themselves and generate new variations. Geographical isolation gradually leads to genetic drift. Continuous accumulation of those variations through a few generations may ultimately lead to the formation of a new species.

(i) Based on the nature, the ecosystem is classified into types namely.
(a) Natural ecosystem: The ecosystem that has been developed in the nature without any human interference is called natural ecosystem. The natural ecosystem is are of two types namely.
(i) Aquatic ecosystem: Aquatic ecosystem occurs in water bodies such as ponds, lakes, rivers, marines, estuaries etc.
(ii) Terrestrial ecosystem: Terrestrial ecosystem: Terrestrial ecosystems occur over land such as forest, grassland, desert etc. 
ecosystem: The ecosystem created and maintained by man to maintain the natural balance by the addition of energy and planned manipulations. Hence, the artificial ecosystems are also called man-made or man-engineered or anthropogenic ecosystem. Examples: Aquarium, garden etc. Agro-ecosystem is the largest man-made ecosystem.
(ii) Based on the duration, the ecosystem is classified into two types namely.
(a) Temporary ecosystem: The ecosystem which are short lived are called temporary ecosystem.
(b) Permanent ecosystem: The ecosystem which are self-supporting natural ecosystem that maintain itself for a longer duration are called permanent ecosystem.
(iii) Based on the size, the ecosystem is classified into two types namely,
(a) Small ecosystem: These are small sized ecosystems which are also termed as micro ecosystems.
(b) Large ecosystem: These are very large sized ecosystems which are also termed as macro ecosystems. 

The metallic oxides which show the properties of acids as well as bases are called amphoteric oxides. It means that they react with both bases and acids to form salt and water.
e.g. ZnO and Al₂O₃
ZnO(s)                         +   2HCl(aq)            \(\rightarrow\) ZnCl₂ (aq)    + H₂O(l)
Zinc oxide (As a base) Hydrochloric acid      Zinc chloride    Water
ZnO(s)                         + 2NaOH(aq)            \(\rightarrow\) Na₂ZnO₂(aq) + H₂O(l)
Zinc oxide (As an acid)  Sodium hydroxide      Sodium zincare   Water

(i) If 3 \(\Omega \) and 6 \(\Omega \) are connected in parallel, thus equivalent resistance of parallel combination
\(=\frac{1}{1/3+1/6}=2\Omega\)
If this combination is connected in series with 2 \(\Omega \) resistance, then total equivalent resistance
= 2\(\Omega \) + 2\(\Omega \) = 4  \(\Omega \)
The resistor connections are as shown below:
(ii) Since, equivalent resistance is less than the least value of resistance (i.e. 2 \(\Omega \)), it means that all three resistors are connected in parallel.
Equivalent resistance \(=\frac{1}{\frac{1}{2}+\frac{1}{3}+\frac{1}{6}}=\)1\(\Omega \)

The part of the hindbrain that takes part in the regulation of respiration is medulla oblongata.

The heat energy obtained in the form of steam from under the earth's crust is called geothermal energy.

(a) Either the seeds bought by her were of pure tall plants (TT) or a hybrid having gene for both tallness and dwarfness (Tt).
(b) If the seeds bought by her had been of pure tall and dwarf type, she would have got both tall and dwarf plants:
(c) In case the seeds are of hybrid tall (Tt) type then 75% of plants will be tall and 25% will be of dwarf type.

Methods of contraception are:
1. Use of condom for penis or for vagina as a mechanical barrier for the sperms to reach the egg.
2. Use of oral pills which change the hormonal balance so that eggs are not released.
3. Surgical method where either the vas deferens of male is blocked or the fallopian tube of female is blocked.

The small number of tigers are causing a worry for the genetics because if they become extinct then the genes of this species will be lost forever. There will be no scope of again getting this species back to life without their genes.

Chlorofluorocarbons (CFCs) are the chemicals which are used in refrigerators and air conditioners as coolant when released into the air react with ozone gas present in the ozone layer and destroy it gradually. If the ozone layer in the atmosphere disappears completely, then all the extremely harmful ultraviolet radiations coming from the sun would reach the earth and cause skin cancer and other ailments in humans, animals and plants.

The mirror formula is \(\frac { 1 }{ v } +\frac { 1 }{ u } =\frac { 1 }{ f } \), where the symbols have standard meaning. When u is changed, v changes, but f remains constant. This is because focal length of mirror depends only on radius of curvature of the mirror.

It regulates the amount of light entering the eye by adjusting the size of the pupil.

(1) By switching off unnecessary lights and fans. This will reduce consumption of coal in production of electricity.
(2) By using public transport such as bus, metro, train etc. as much as possible. This will reduce consumption of petrol and diesel.
(3) By repairing leaked water taps. We can save water by following this method. This will save energy that is spent during treatment and pumping of water.
(4) Reusing used paper, envelopes, etc. This will save the trees from which paper is made; it will also save energy spent on making and recycling papers.

Oxidation

Voluntary actions are under the control of our will, it needs thinking. e.g. talking, walking. Involuntary actions are not under the control of our will, they are automatic. eg. salivation, heart beat.

\(\therefore\) Current, \( I=\frac{P}{V}=\frac{2000 \quad W}{220 \quad V}>5A\)
Since, current drawn by oven is greater than the rated value of current, which may cause overloading and excessive heating of the circuit.

(a) The solar cells are costly and hence the energy available from them expensive.
(b) 15 km/h is the minimum wind velocity required to obtain useful energy with a windmill.
(c) Nuclear fission is the process in which a radioactive atom splits up into smaller nuclei when struck with low energy neutrons.

(i) Magnesium reacts with water only on boiling.
(ii) Copper metal does not react even with steam.

The different constituents of blood are plasma (the fluid part of the bloo(d) and blood corpuscles consisting of RBCs, WBCs, and platelets)
WBCs are known as the soldiers of the body because they fight against the pathogenes that invade our body, thus preventing the occurence of diseases.

The major differences between an electric motor and generator are stated below:
Electric Motor:
1. It converts electrical energy into mechanical energy.
2. It needs electrical energy for its works.
3. They are used as water pumps, marble grinders etc.
Generator:
1. It converts mechanical energy into electrical energy
2. It needs mechanical energy for its working.
3. They are used as water pumps, marble grinders etc.
4. diesel generator, hydro-electric generator are the examples of it.

The total amount of fresh water is more than enough to meet the needs of human  beings. But due to its uneven distribution, wide seasonal as well as yearly fluctuation in rainfalls and wastage water shortage is a chronic is a chronic problem in most parts of the world.

(i) The symbols of elements are arranged in increasing order of their atomic number as shown in the below figure

(ii) The symbols of elements are arranged in increasing order of their group numbers as follows: