(1). Give three important features of fossils which have helped in the study of evolution.
(2). How does taxonomy support evolution?
Question: 21. What do you mean by linear magnification produced by mirrors? The power of a lens is +2.5 D. What kind of lens is it and what is its focal length?
Draw a ray diagram of an image when an object is placed on the principal axis of a convex lens between focus and optical centre.
- Convex lens (converging lens)
P = + 2.5 D, f = 1/p = 1/2.5 m = 100×10/2.5 = +40 cm
- When an object is placed between focus and optical center of the convex lens then the Image will be virtual, magnified, erect.
In order to study the properties of HCl acid, a student adds dilute HCl to a test tube containing a compound X. As a result a colorless and odorless gas is evolved, Which turns the lime water milky. What could be the compound X? Name the gas formed. What would happen on passing the gas in excess of lime water? 
Answer: ‘X’ can be sodium carbonate. The gas formed is CO2gas.
When CO2gas is passed in excess through the lime of water, then milkiness disappears.
(1) State two advantages of parallel circuit over series circuit.
(2). In a given ammeter, a student sees that needle indicates 17 divisions in ammeter while performing an experiment to verify Ohm’s law. If ammeter has 10 divisions between 0 to 0.5 A, then what is the value corresponding to 17 divisions? 
Answer: (2). Least count of ammeter is = 0.05A,
So Value of 17 divisions = 17 × 0.05 = 0.08 Ampere.
Question: 24. Figures show three cylindrical copper conductors with face areas and lengths. If same p.d. is applied across each, then compare the current passing through each conductor. 
∴ So, Same current flows through conductors P and Q. Current through conductor R is 1/3rd times the current through P or Q conductors.
A student while verifying Ohm’s law calculated the value of resistance of resistor for each set of observation. However, the values of resistance were slightly different from the actual value. Is his experiment wrong? Justify your answer.
Question: 25. (a). Acetic acid, when dissolved in water, it dissociates into reversely. Why?
(b). Give the reaction involved. 
Answer: (a). As acetic acid is a weak acid and does not ionise completely into its ions.
Question: 26. When light from free space bends towards normal, on hitting a surface, then what should be its refractive index (μ)? Is μ > 1, μ < 1 or μ = ½? Justify your answer. 
Answer: μ > 1, As free space has refractive index = 1. Ray is bending towards normal thus μ of medium is greater than 1.
Question: 27. Which is not a vegetative propagation in the following answers? Give the reason for your answer. 
Answer: Option (D) is not vegetative propagation since it shows budding in hydra.