CBSE Last Year Question Paper Of Science For Class 9th (2020) with solutions PDF

Last Year Question Paper of Science For Class 9th (2019-20) Download With Solutions

                                                                 Section A 

Q.1 choose the correct option:        (5x1) 

(1) The electron distribution in an aluminum atom . 

     (a) 2, 8, 3  (b) 2, 8, 2  (c) 8, 2,3  (d) 2,3,8

A.  (a) 2,8,3

(2) What is acceleration for the free fail object?

      (a) 8.9 ms-2 g  (b) 9.8 ms-2  (c) 98.1 ms-2  (d) none of the above.

A.  (b) 9.8 ms-2

 (3) Which one of the following is not the unit of the energy? 

       (a) Joule  (b) Nm  (c) KW  (d) KWh

A.  (d) KWh 

(4) If a wave complete 20 vibrations in 2.5 seconds,then its frequency will be : 

       (a) 8 Hz  (b) 20 Hz  (c) 50 Hz  (d) 200 Hz

A.  (a) 8Hz

 (5) The conversion of NO3 to free nitrogen is called: 

      (a) Nitrification  (b) Denitrification  (c) Ammonification  (d) Nitrogen fixation 

A. (b) Denitrification

Q.1 Name the three subatomic particle of an atom.

A. Electron, Proton, Neutron

 Q.2 What is gravitational force ? Write its formula.

A. The force between the object and the earth is called gravitational force.

     Formula:-    F = G Mm/ r^2

        

Q.3. Define 1 joule.

A. When 1 N force exerts on an object and it displaces at distance 1 m is called 1 Joule.

 Q.4 what is the audible range of the sound of human ear? 

A.  20 Hz - 20,000 Hz

Q.5 What is green house effect ? Write the name of green house gases. 

A. The increase in percentage of such gases which cause to increase the temperature of the earth.

   Green House Gases:- Co2, N2O, CFC, Hydrofluorocarbons (includes HCFCs and HFCs)

                                                         Section B

 Q.1 Write application of Archimedes Principle.

A.  (i) Hydrometer (Determine the density of the liquid)

      (ii) Lactometer (Determine the purity of the milk)

      (iii) Designing ships and submarines.

Q.2 Write two differences between mass and weight.

A.   

Mass is a property of matter. The mass of an object is the same everywhere.	Weight depends on the effect of gravity.
Mass can never be zero.	Weight can be zero
Mass does not change according to location.	Weight varies according to location.
Mass is a scalar quantity	Weight is a vector quantity
Mass measured in KG	Weight is measured in Newton

Q3 An electric bulb of 60 W is used for 6 hours per day. Calculate the units of energy consumed in one day by the bulb ? 

A.  Power =  60 W ⇒ 60 ➗ 1000 ⇒  0.06 KWh
      Time = 6 hours
       
       Energy = Power x Time
                     = 0.06 x 6
                     = 0.36 Unit
 Bulb consumes 0.36 unit in one day

Q.4 (i) Draw a sketch of Bohr's model of an atom with 4 shells. 

A.  For Bohr’s model with 4 shells, the electrons no. are as follows:

First shell: 2 electrons

Second shell: 8 electrons

Third shell: 18 electrons

Fourth shell: 18 electrons

But maximum electrons in any shell can only be 8 due to octet rule.

(ii) Write the distribution of electrons in carbon and sodium atom.

Distribution of electron in Carbon 

K  L

2, 4

Distribution of electron in Sodium

K   L   M

2,  8,  1

Q.5 Write the effect of air pollution .

A. 

Pollutant	Health effects at very high levels
Nitrogen Dioxide, Sulphur Dioxide, Ozone	These gases irritate the airways of the lungs, increasing the symptoms of those suffering from lung diseases
Particles	Fine particles can be carried deep into the lungs where they can cause inflammation and a worsening of heart and lung diseases
Carbon Monoxide	This gas prevents the uptake of oxygen by the blood. This can lead to a significant reduction in the supply of oxygen to the heart, particularly in people suffering from heart disease

  

                                                               Section C 

Q.1 Explain with examples. 
(i) isotopes 
(ii) isobars
(iii) Valency 

A. (i) Elements with the same atomic number but different mass numbers are called isotopes. Eg.- Isotopes of hydrogen: Protium (A = 1), Deuterium (A = 2), Tritium (A = 3). This is because of presence of more neutrons.

(ii) Elements with same mass numbers but different atomic numbers are called Isobars. Eg.- Potassium isotope (K-40) and Calcium (A = 40). These are always different elements, and almost always involve an isotope.

Valency is the tendency of an element to give / take electrons to complete an octet.