CBSE Class 10 Science 2012 Question Paper

Name the functional group present in each of the following organic compounds : (i) $C_2H_5Cl$ (ii) $C_2H_5OH$

What will be the colour of the sky when it is observed from a place in the absence of any atmosphere ?

Which class of chemicals is linked to the decrease in the amount of ozone in the upper atmosphere of the earth ?

Bacteria and fungi are called decomposers. Why ?

How can the valency of an element be determined if its electronic configuration is known ? What will be the valency of an element of atomic number 9 (nine) ?

An element 'X' has atomic number 13 : (a) Write its electron configuration. (b) State the group to which 'X' belongs ? (c) Is 'X' a metal or a non-metal ? (d) Write the formula of its bromide.

State one genetically different feature between sperms and eggs of humans. What is its consequence ?

List two advantages of vegetative reproduction practised in case of an orange plant.

List four properties of the image formed by a plane mirror.

When we place a glass prism in the path of a narrow beam of white light a spectrum is obtained. What happens when a second identical prism is placed in an inverted position with respect to the first prism ? Draw a labelled ray diagram to illustrate it.

A star sometimes appears brighter and some other times fainter. What is this effect called ? State the reason for this effect.

List four advantages of water stored in the ground.

“Burning fossil fuels is a cause of global warming.” Justify this statement.

What are isomers? Draw the structures of two isomers of butane, $C_4H_{10}$. Why can’t we have isomers of first three members of alkane series?

F, Cl and Br are the elements each having seven valence electrons. Which of these (i) has the largest atomic radius, (ii) is most reactive? Justify your answer stating reason for each.

Explain the meaning of sexually transmitted diseases (STDs). Give two examples of STDs each, caused due to (i) bacterial infection and (ii) viral infection. State in brief how the spread of such diseases may be prevented.

A blue colour flower plant denoted by BB is crossbred with that of white colour flower plant denoted by bb. (a) State the colour of flower you would expect in their F1 generation plants. (b) What must be the percentage of white flower plants in F2 generation if flowers of F1 plants are self-pollinated ? (c) State the expected ratio of the genotypes BB and Bb in the F2 progeny.

What is meant by the term speciation ? List four factors which could lead to speciation.

Distinguish between homologous organs and analogous organs. In which category would you place wings of a bird and wings of a bat ? Justify your answer giving a suitable reason.

State the type of mirror preferred as (i) rear view mirror in vehicles, (ii) shaving mirror. Justify your answer giving two reasons in each case.

The image of a candle flame placed at a distance of 45 cm from a spherical lens is formed on a screen placed at a distance of 90 cm from the lens. Identify the type of lens and calculate its focal length. If the height of the flame is 2 cm, find the height of its image.

A student cannot see a chart hanging on a wall placed at a distance of 3 m from him. Name the defect of vision he is suffering from. How can it be corrected ? Draw ray diagrams for the (i) defect of vision and also (ii) for its correction.

What is the difference between the chemical composition of soaps and detergents? State in brief the action of soaps in removing an oily spot from a shirt. Why are soaps not considered suitable for washing where water is hard ? Or List in tabular form three physical and two chemical properties on the basis of which ethanol and ethanoic acid can be differentiated.

Define the terms pollination and fertilisation. Draw a diagram of a pistil showing pollen tube growth into the ovule and label the following : pollen grain, male gamete, female gamete, ovary. Or Describe in brief the role of (i) testis (ii) seminal vesicle, (iii) vas deferens, (iv) ureter and (v) prostate gland in human male reproductive system.

List the sign conventions for reflection of light by spherical mirrors. Draw a diagram and apply these conventions in the determination of focal length of a spherical mirror which forms a three times magnified real image of an object placed 16 cm infront of it. Or State the law of refraction of light that defines the refractive index of a medium with respect to the other. Express it mathematically. How is refractive index of any medium ‘A’ with respect to a medium ‘B’ related to the speed of propagation of light in two media A and B ? State the name of this constant when one medium is vacuum or air. The refractive indices of glass and water with respect to vacuum are 3/2 and 4/3 respectively. If the speed of light in glass is $2 \times 10^8$ m/s, find the speed of light in (i) vacuum, (ii) water.

The colours of aqueous solutions of $CuSO_4$ and $FeSO_4$ as observed in the laboratory are :

A student prepared an aqueous solution of $CuSO_4$ in beaker X and an aqueous solution of $FeSO_4$ in beaker Y. He then dropped some iron pieces in beaker X and some zinc pieces in beaker Y. After about 10 hours he observed that the solutions in X and Y respectively appear:

Which of the following observations is true about dilute solution of acetic acid?

A student takes $Na_2CO_3$ powder in a test tube and pours some drops of acetic acid over it. He observes :

A student adds 4 mL of acetic acid to a test tube containing 4 mL of distilled water. He then shakes the test tube and leaves it to settle. After about 10 minutes he observes :

To determine focal length of a concave mirror a student obtains the image of a well lit distant object on a screen. To determine the focal length of the given concave mirror he needs to measure the distance between :

A student obtained a sharp image of the grills of a window on a screen using a concave mirror. His teacher remarked that for getting better results a well lit distant object (preferably the sun) should be focussed on the screen. What should be done for this purpose?

To determine the focal length of a convex lens by obtaining a sharp image of a distant object we generally follow the following steps which are not in proper sequence. (a) Hold the lens between the object and the screen (b) Measure the distance between the lens and the screen (c) Select a well lit distant object (d) Place a screen opposite to the object on the lab table (e) Adjust the position of the lens to form a sharp image. The correct sequence of these steps is :

A student traces the path of a ray of white light through a rectangular glass slab and marks, the angles of incidence (∠i), refraction (∠r) and emergence (∠e) as shown. Which angle or angles has he not marked correctly ?

While tracing the path of a ray of light passing through a rectangular glass slab a student tabulated his observations as given below : | S. No. | ∠i | ∠r | ∠e | | :--- | :--- | :--- | :--- | | I | 60° | 40° | 61° | | II | 50° | 36° | 51° | | III | 40° | 28° | 39° | | IV | 30° | 20° | 31° | The correct observation is :

A student has to observe a permanent slide of binary fission in amoeba. Find the correct sequence of steps given below for focussing the object under a microscope. (a) Place the slide on the stage, look through the eye-piece and adjust the mirror to get proper illumination. (b) Focus the slide sharp using fine adjustment screw. (c) Look through the eye-piece and raise the objective lens using coarse adjustment screw till the object is focussed. (d) Look through the eye-piece and move the slide till the object is visible.

After viewing different slides, a student draws following diagrams. Select the one which depicts binary fission in amoeba.

After observing the prepared slides of binary fission in amoeba and budding in yeast following observations were reported : (a) Single cells of amoeba and yeast were undergoing binary fission and budding respectively. (b) Cytokinesis was observed in the yeast cell. (c) Elongated nucleus was dividing to form two daughter nuclei in amoeba. (d) A chain of buds were observed due to reproduction in amoeba. The correct observation(s) is /are :

A student after viewing a prepared slide illustrates the budding in yeast in the following order which is not correct : (a), (b), (c), (d), (e). The correct order should be :

Dry raisins were soaked in water for 2 hours, to determine the percentage of water absorbed by raisins. Before final weighing of swollen raisins, the extra water left on the surface of soaked raisins was removed by :

While performing the experiment with raisins to determine the percentage of water absorbed by them, a student made following measurements : Mass of water in the beaker = 40g; Mass of raisins before soaking = 5g; Mass of raisins after soaking for 2 hours = 8g; Mass of water left in the beaker after the experiment = 35g. The percentage of water absorbed by raisins is :