Zinc will react with copper oxide to displace copper. Magnesium will also displace zinc from zinc oxide and copper fromn copper oxide. Copper, being least reactive will not react with any of the given oxides.

Fore brain

According to this rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic field and the second finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.

(a) Limitation of wind energy:
Wind energy cannot be harnessed at places where wind speed is not at least 15 km/h.
(b) Limitation of tidal energy:
The rise and fall in sea water during a high tide or a low tide is not good enough to generate electricity on a large scale.

The major events during photosynthesis are
(i)absorption of light energy by chlorophyll
(ii)Conversion of light energy to chemical energy
(iii)splitinh of H₂,O₂ and e^-
(iv)reducing of CO₂ to carbohydrates

This is because, water does not provide energy to multiply whereas sugar provides energy for the yeast to undergo multiplication.

RrYy (Round yellow).

50%

Vegetarian habit is safer. Being closer to producers, less DDT will accumulate in our body. Bio magnification leads to higher level of DDT in higher trophic levels.

Stars twinkle due to atmospheric refraction of starlight. The starlight passes through different layers of atmospheric medium of gradually changing refractive index. So, it is refracted multiple times. As the apparent position of star and the physical condition of the earth's atmosphere are not constant the amount of starlight entering the eye flickers and gives a twinkling effect.

Different colours travel through prism with different speeds and have different refractive index

Given
\(n_g={3\over 2},\ \ \ \ n_w={4\over 3}\)
Speed of light in glass=2 x 10⁸ m/s
Speed of light water = v = ?
\(n_g={Speed\ of\ light\ in\ air\over Speed\ of\ light\ in\ glass}\)
\(\Rightarrow\ \ {3\over2}={Speed\ of\ light\ in\ air\over 2\times10^8\ m/s}\)
Speed of light in air=\({3\over 2}\times2\times10^8=3\times10^8\ m/s\)
\(n_w={Speed\ of\ light\ in\ air\over Speed\ of\ light\ in\ water}\)
\(\Rightarrow\ \ {4\over 3}={3\times10^8\ m/s\over V}\)
\(3\times10^8\times{3\over4}=v\)
⇒ v=2.25 x 10⁸ m/s

(1) Forest resources should be used in an environment friendly and developmentally sound manner.
(2) Instead of using non-renewable natural resources, use of renewable natural resources should be preferred.
(3) Waste water generated by industries should be recycled.

Given, P₁ = 250 W, P₂ = 1200 W,
t₁ = 1h = 3600 s, t₂ = 10 min = 600 s
\(\therefore\) Energy
Q₁ = P₁t₁ = 250 \(\times\)3600 = 900000 J = 900 kJ
and Q₂ = P₂t₂ = 1200 \(\times\) 600 = 720000 J = 720 kJ
Thus, TV set uses more energy.

(a) The solar cooker box is covered with a plane glass plate so as to prevent heat from escaping.
(b) Sun is said to be the ultimate and the original source for most of the energy present on the earth. When sun rays fall on oceans and other water bodies, the water present in the water bodies gets evaporated and rises up in the atmosphere. In the upper part of the atmosphere, this water vapour gets condensed and forms douds, which give rain on the high lands. Therefore, the rain water runs over the Sand surface towards the large water bodies. This running water over the land surfaces is called river. Therefore, the energy of running water actually originates from the solar energy. This is why solar energy of water flowing in a river is considered to be an indirect form of solar energy.
(c) The fission of nucleus is brought about by splitting the nucleus of heavy atoms, such as uranium or plutonium, with low-energy neutron bombardment. 

(i) Oxygen enters the human body through the nasal passage and reaches the lungs.
(ii) Numerous alveoli are present in the lungs. These alveoli are surrounded by many blood capillaries. From the alveoli, 0₂ is taken up by the red blood cells present in the blood capillaries.
(iii) Similarly, the CO₂ from the various tissues is transported to the alveoli.
(iv) This CO₂ is then released through the nasal passage during exhalation. Alveoli are the sites of exchange of gases. Each lung contains 300- 350 million alveoli.
These alveoli increase the surface area for gaseous exchange, making the process of respiration more efficient.

The two ways in which non-biodegradable substances would affect the environment are
(i) They make the environment poisonous and unfit for survival of living forms of life.
(ii) They block the transfer of energy and minerals in the ecosystem.

Electromagnetic Induction: When a conductor is set to move inside a magnetic field or a magnetic field is set to be changing around a conductor, electric current is induced in the conductor. This is just opposite to the exertion of force by a current carrying conductor inside a magnetic field. In other words, when a conductor is brought in relative motion vis-a-vis a magnetic field, a potential difference is induced in it. This is known as electromagnetic induction.

Activity:
- To demonstrate electromagnetic induction Materials Required:
- A galvanometer, coil, bar magnet and some wires.
Procedure:
- The coil is inserted over a hollow tube of cardboard.
- With the help of wires, the two ends of the coil are attached to the galvanometer.
- The north pole of the bar magnet is moved towards the end 'B' of the coil.
- It is observed that the galvanometer needle shows deflection to right.
- When the magnet is moved away from the coil, the galvanometer needle shows deflection towards left.
- When the magnet is in static position, no deflection is seen in galvanometer needle.
- Induction of electric current in the coil is the cause of deflection in galvanometer needle.
- If the magnet is kept stationary and coil is moved, then also the galvanometer needle shows deflection.
Conclusion:
- When the coil and the bar magnet are in relative motion, a current is induced in the coil.

(a)

(b) \(\underset{Ethanol}{CH_3CH_2OH}\xrightarrow[443k]{conc. H_2SO_4}\underset{Ethene}{CH_2=CH_2}+H_2O\)

(1) A food web is formed by interlinked of food chains and also so it is not straight.
(2) A food web provides alternative pathways of the availability of food.
(3) A food web helps in checking the over-population.
(4) A food web helps in the development of an ecosystem..

(i) If H⁺ ion concentration is more, pH will be less and vice versa or pH of a solution is inversely proportional to H⁺ ion concentration or pH 52 log (H⁺).
(ii) This solution is neutral.
(iii) 1MNaOH solution.
(iv) When the pH in the mouth is below 5.5, bacteria present in the mouth produce acids by degradation of sugar and corrode the tooth enamel. It can be prevented by using tooth pastes which are generally basic.
(v) As hydronium [H₃O]⁺ ion.

(a) Eka-silicon for germanium (Ge) and eka-aluminium for gallium(Ga).
(b) Group number of Ga is 13 and its period is 4th and group number of Ge is 14 and its period is also 4th.

(c) Both Ga and Ge are metalloids.
(d) Ga lies in group 13, therefore, it has 13 - 10 = 3 valence electrons. Similarly, Ge lies in group 14 and hence it has 14 - 10 = 4 valence electrons.

(a) recharging the ground water
(b) can be used for irrigation
(c) treated municipal water can be used for washing cars, watering the gardens
(d) certain pollutants in sewage water can be become fertiliser for various crops.