Question: 16. Compose an activity to arrange Ca, Mg and Fe metals in the decreasing order of reactivity with water. Write suitable balanced chemical equation and draw diagrams. 
(1). Draw a well-labelled diagram of human alimentary canal. 
(2). Discuss nutrition in amoeba with the help of a diagram.
(1). What is fragmentation in organisms? Name a multi cellular organism which reproduces by this method.
(2). What is regeneration in organisms? Describe regeneration in Plan aria with the help of a suitable diagram.
(1). Design an activity with the help of two nails, a very thin aluminium strip, a 12 V Battery and a key to illustrate how electric fuse works. 
(2). Cable of a microwave oven has three wires inside it which have insulation of different colors black, green and red. Mention the significance of the three colors and the potential difference between red and black one.
Answer: (2). Red colour is for Live wire. Black colour for Natural wire. Green colour for the Earth wire. P.D. between Red and Black wire is 220 volts.
(1). Define 1 watt. 
(2). State the commercial unit of electric energy. Express it in terms of SI unit of energy.
(3). An electric refrigerator rated as 750 W operates 8 hours per day. What is the cost of the energy to operate it for the month of June at Rs. 2.50. per kWh?
Answer: Cost of 180 kWh = Rs. 450.00.
Question: 19. Ethanoic acid reacts with sodium hydrogen carbonate to produce a salt ‘X’ and a gas ‘Y’. Identify ‘X’ and ‘Y’ and write their chemical names. With the help of a labelled diagram describe an activity to confirm that the gas ‘Y’ is correctly identified by you. Also write the chemical equation of the reaction involved. 
Answer: X: CH3COONa, Sodium ethanoate; ‘Y’: CO2 , Carbon dioxide
A diagram showing passage of CO2 through lime water.
CH3COOH + NaHCO3 → CH3COONa + CO2 + H2O Or Ca(OH)2 + CO2 → CaCO3 + H2O
(1) What is a soap? Why are soaps not suitable for washing clothes when the water is hard?
(2) Explain the action of soap in removing an oily spot from a piece of cloth.
Question: 20. Draw diagram of human female reproductive system and label on it the parts the perform the following functions: 
(1). Carry eggs from ovary to uterus.
(2). Where the fertilized egg gets implanted.
Explain the role played by placenta in providing nutrition to a growing embryo due to its special design.
Question: 21. A student focused the flame of a candle on a screen with the help of a convex lens. He noted the positions of candle, lens and screen on the scale as given below:
Position of candle = 14.0 cm, Position of convex lens = 50.0 cm
Position of screen = 86.0 cm
(i). Find the focal length of the lens.
(ii). If under the given condition, height of the flame is 1.5 cm, what would be the height of image obtained on the screen?
(iii). If he displaces the candle to 32.0 cm, where will the image be formed and what will be its nature? Give reason for your answer.
(iv). After this if he further displaces the candle towards the lens, what will be the nature of the image formed and where will it be?
(v). Draw a ray diagram to show the formation of image in the above mentioned case (iv).
- u = (50 – 14) cm = 36 cm; v = (86 – 50) cm = 36 cm, Thus object is at 2f. Therefore f = 18 cm
- Height will be same, i.e., 1.5 cm
- u = 50 – 32 = 18 cm. Thus, object will be at focus. Therefore, image will be at infinity and is real, inverted and enlarged.
- Object will come in between focus and optical centre.
Image will be virtual, erect and enlarged and formed on the same side of lens as the object.