Solved Board Paper For CBSE Class 10 Science

Baking powder should be added to a cake to make it soft and fluffy. It is mixture of sodium carbonate and tartaric acid (a mild acid).

Acids produce H⁺ ions only in the presence of water and thus can show acidic behaviour only in the presence of water. Therefore, dry HCl gas does not turn blue litmus paper red.

Iron is more reactive than copper and hence it displaces copper from its salt solution (copper sulphate). Thus, colour of the copper sulphate solution changes from blue to dirty green.

-2.5 = 1/f

f = -1/2.5

f = -0.4 m

(i)Since unsaturated hydrocarbons undergo addition reaction, ethene being unsaturated hydrocarbon will undergo addition reaction.

(ii) Ethanoic acid (Since its formula is CH₃COOH).

R = V/I

R = 220/5

R = 44 ohm

Number of resistors of 264 ohm that are required to make an effective resistance of 44 ohm = n

n x 1/264 = 1/44

n = 264/44

n = 6

Hence 6 resistors of 264 ohm (in parallel) are required to carry 5 A on a 220 V line.

(a) ZnO + C Zn + CO (Oxidation-Reduction reaction)

(b) BaCl₂ + Na₂SO₄ BaSO₄ + 2NaCl (Double displacement reaction)

The amount of heat produced in a wire or material is given by the formula

H= I²Rt

This is known as Joule’s law of heating.

(a) Reaction between water and acid is a highly exothermic. During this reaction a large amount of heat is generated that can cause splashing of the mixture and burns if water is added quickly to a concentrated acid. In order to prevent this, acid is added to the water slowly with constant stirring.
(b) Bacteria present in the mouth produce acids by degrading sugar and food particles left in the mouth after eating. This can corrode teeth enamel. Thus, in order to neutralise excess acid in the mouth and prevent tooth decay, toothpastes are made basic.
(c) Plaster of Paris absorbs water molecule to form a hard solid mass of gypsum and then it cant be used for supporting fractured bons. Therefore, it should be stored in a water proof container.

Potential difference (V) = 1.5 x 3

V = 4.5 volt

Resistance (R) = 5 ohm

Current in the circuit (I) = V/R

I = 4.5/5

I = 0.9 ampere

(c) The zygote formed will have XY chromosomes and hence the zygote will be a male.

Deoxygenated blood enters the right atrium of the heart through vena cava. It is then pumped to right ventricle through atrio-ventricular aperture. It is then taken to the lungs for oxygenation via pulmonary artery. The oxygenated blood from the lungs returns back to the left atrium of the heart. It is then pumped to left ventricle which pumps it into aorta. Aorta carries the blood to different body parts.
Deoxygenated blood in right atrium Deoxygenated blood in right ventricle Deoxygenated blood in pulmonary artery lungs Oxygenated blood in left atrium Oxygenated blood in left ventricle Oxygenated blood in aorta body parts

(a) (i)Coin get dissolved in solution.

(ii)Colour of solution turn blue due to the formaIon of Cu(NO₃)₂

(iii) Cu + 2Ag NO₃ Cu (NO₃)₂ + 2Ag

(b)(i)Trivalent metal could be Fe, Al, But Al is must abundant metal in earth’s crust. So metal is Aluminium (Al).

(ii)(1) Al foil is used in packaging food.

(a) (i) Ionic

(ii) AC₂

(b)Since element X forms XO with oxygen it means the valancy of element X is 2. When X is made to combine with chlorine the formula of compound will be XCl₂ and with S it will give XS.

(c) It is the process of depositing a layer of Zinc over iron to prevent it fromv rusting.

(a) 1. Sun is visible to us about 2 minutes before the actual sunrise because of atmospheric refraction.

2. The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light. These are more effective in scattering light of shorter wavelengths at the blue end than light of longer wavelengths at the red end. The red light has a wavelength about 1.8 times greater than blue light. Thus, when sunlight passes through the atmosphere, the fine particles in air scatter the blue colour (shorter wavelengths) more strongly than red. The scattered blue light enters Our eyes and colour of sky appears blue.
(b).

(a) (i) Distance of the object from the lens (u) = - 20 cm
Distance of the image from the lens (v) = 30 cm
Focal length of the lens = f
According to Lens formula,
1/v – 1/u = 1/f
or,1/30 – 1/(-20) = 1/f
or,1/30 + 1/20 = 1/f
or,(2+3)/60 = 1/f
or,5/60 = 1/f
or,f = 12 cm
Since the focal length is positive, the lens is a convex lens with focal length 12 cm.
(ii) Size of the object = h
Size of the image = h’.
We have the relation for magnification of lens,
m=v/u=h’/h
or,h’ = (30 x 2.5)/(-20)

or,h’ = -3.75
Hence the image formed is real, inverted and 3.75 cm tall.
(iii)

(b) Concave mirror is used as reflector in head lights of vehicles.
(c) Convex mirror is used as rear-view mirror in automobiles.

Image is formed between the focus and the optical centre of the concave lens.

(a) (i) As the pH value increases the concentration of hydrogen ion decreases. Thus, solution B with pH value 5 has higher hydrogen ion concentrations.

(b) The common name of Na₂CO₃.10H₂O is washing soda.

Energy consumed is given by the relation, E = P x T

Energy consumed by the 100 watt bulb in 30 days is given by,

Similarly energy consumed by four 40 watt bulbs,

Hence, total energy consumed = 6 kWh + 19.2 kWh = 25.2 kWh.

1 2 1

(i) Yellow coloured seeds are expected in the F1 progeny as in this case yellow colour is dominant over green colour.
(ii) The self pollination of plants of F1 generation yields plants in the ratio of 3 (dominant):1 (recessive). Hence when F1 plants are self pollinated, the percentage of green coloured seeds will be 25%.
(iii) The genotypes YY and Yy will be found in the ratio 1:2.

(a) Ca(s) + 2H₂O(l) → Ca(OH)₂ (aq) + H₂(g)

(b) K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g) +heat

(c) Zn(s) + 2HCl (dil)→ ZnCl₂(aq) + H₂(g)

In a double displacement reaction, exchange of ions takes place among the reactants, while in displacement reaction more reactive metal displaces less reactive metal from its salt.

Example of displacement reaction:
Fe + CuSO₄Cu + FeSO₄

Here, Fe displaces Cu from CuSO₄ because Fe is more reactive than Cu.

Example of double displacement reaction:
BaCl₂ (aq) + Na₂SO₄(aq)2NaCl (aq) + BaSO₄(s)

Here, exchange of ions between reactants takes place.

1. strength of the magnetic field in which conductor is placed.
2. strength of current flowing through the conductor.
3. length of conductor.

(i)

(ii) Applying mirror formula

(iii) Image is virtual and erect.

Fermentation :
It is the process in which sugar molecules and starch molecules are broken down by the action of enzymes into smaller molecule ethanol and carbon dioxide.

The fermentation of sugar is carried out at a controlled temperature of 20ºC to 30ºC. Fermentation produces a dilute solution of ethanol in water. Ethanol is separated from water and purified by the process of distillation.
Uses :
1. Ethanol is used for making antifreeze mixtures.
2. Ethanol is used as fuel in internal combustion engine and in spirit lamps.
Harmful effects of drinking alcohol :
a. Ethanol is harmful for lungs and causes addiction.
b. Ethanol can create heart problems.
c. It effects on the nervous system.

The student must note the following observations:

(a) Immediate fizzing occurred on adding sodium hydrogen carbonate to ethanoic acid.

(b) A colourless gas (carbon dioxide) evolved due to the reaction of sodium hydrogen carbonate to ethanoic acid. At the end of the reaction, a colourless solution obtained.

The process is budding.

(i) No change in colour is observed.

(ii) No change in colour is observed.

(iii) The colour of solution turns orange.

(iv) Evolution of a colourless and odorless gas with brisk effervescence is observed.

(i)As the distance between the object and the lens decreases, the distance between the lens and the image increases. Therefore, in order to obtain the image on the screen, he has to move the lens away from the screen.

(ii) In case of a convex lens, the size of the image increases as the distance between the object and the lens decreases.

(iii) When an object is placed between the focus and the optical centre of a convex lens, the image formed is virtual and erect. A virtual image is not obtained on the screen. Thus, when the object is placed very near to the convex lens, it will disappear from the screen.

Below given is the ray diagram in which the ray EF is the incident ray and GH is the emergent ray which is parallel to the incident ray.