List of top Science Questions

During urine formation, tubular reabsorption and secretion take place in the kidneys. Which of the following sets correctly indicates both the substances that are reabsorbed in the kidneys?

Assertion (A): The rate of breathing in aquatic organisms is much lower than in the terrestrial organisms.
Reason (R): The amount of oxygen dissolved in water is less as compared to the amount of oxygen in air.

In a controlled experiment, the anthers of a mustard plant's flowers were carefully removed in the bud stage before they matured. The bud was covered with a paper bag.
What will be the most likely result for these flowers?

The Vas deferens and the Oviduct are both targets for surgical contraception (Vasectomy and Tubectomy respectively). Analysing the process of reproduction, what common biological event is prevented by blocking both these structures?

The male gamete of an apple plant has seventeen chromosomes. What is the number of chromosomes in the female gamete and in the cells of the adult plant respectively?

A student wants to determine the focal length of a convex lens using sunlight. Which of the following practical procedures will give the most accurate result?

Assertion (A): The apparent depth of a coin in water is less than its real depth.
Reason (R): Light bends away from the normal when it travels from water to air.

Electrical wires made of aluminum

Rishita summarizes the chlor-alkali process in the following table.

Option	Product	Formed	Use
I	Hydrogen	At cathode	Used as a fuel
II	Chlorine	At anode	Used to make margarines
III	Sodium Hydroxide	Near cathode	To make soap
IV	Sodium Hydroxide	Near anode	To make bleaching powder

Identify the options that are correctly matched.

Which of the following salts contain water of crystallisation:
(i) Plaster of Paris, (ii) Washing soda, (iii) Baking soda and (iv) Gypsum.

The following question consists of two statements: Assertion (A) and Reason (R). Answer this question by selecting the appropriate option given below.
Assertion (A): Onion extract loses its smell, when it is added to baking soda solution whereas it retains its smell when added to lemon juice.
Reason (R): Onion acts as an olfactory indicator.

An electrical appliance rated 1000 W is operated at 250 V. What current does it draw?

A food label is given below. E304 and E307b are added to the flavoured biscuits.

Which of the following is added to food packets for the same reason?

B.
I. What is dispersion of light?
II. Which colour of light deviates the least during dispersion through a prism?
III. State why the sky appears dark to an astronaut in outer space.
IV. Draw a simple labelled diagram to show how white light splits into different colours while passing through a glass prism.

A.
I. What is meant by accommodation of the human eye?
II. What is the near point of a normal eye and what does it signify?
III. Name which type of lens is used to correct the defect in which a person cannot see distant objects clearly.
IV. Draw a diagram to show how the choice of your lens in (d) helps to see distant objects clearly?

The figure shows a circuit with a 15 V battery connected to several resistors. Using the given circuit diagram:
A. Find the total current supplied by the battery.
B. Calculate the potential difference between points A and B.

A. State Snell's Law of refraction.
B. Define the refractive index of a material with respect to another material giving the mathematical expression.

A concave lens forms an image that is 1/3rd the size of the object, as shown in the diagram. If the object is placed 24 cm in front of the lens, determine:
A. the type of lens.
B. the image distance
C. the focal length of the lens

I. State Joule's Law of heating.
II. What happens to the heat produced in a conductor if the resistance is doubled while keeping other variables constant?

I. Define resistivity.
II. Justify with an example why resistivity is an intrinsic property of a material.

A. State the Right-Hand Thumb Rule and describe how it helps determine the direction of magnetic field around a current-carrying conductor.
B. Explain how the magnetic field changes with distance from the conductor.

I. Refer to the dialogue between Alisha, Drishti and Bhushan in the chemistry lab. They are discussing rusting of iron and formation of ammonia gas. Who all do you agree with and why?
Alisha: The formation of ammonia by reaction of nitrogen with hydrogen is a reduction reaction.
Dristhi: Both rusting of iron and formation of ammonia are redox reactions.
Bhushan: Rusting of iron is an oxidation reaction.
II. Assess the following chemical equations. Identify the error(s) and rewrite the equation after correction.
(i) \(\mathrm{MgCl_2 + AgNO_3 \to AgCl_2 + MgNO_3}\)
(ii) \(\mathrm{Al + H_2SO_4 \to Al_2SO_4 + H_2O}\)

I. Refer to the dialogue between Daljeet and Avik in the chemistry lab. They have learnt about decomposition reactions. Who has understood decomposition reactions correctly? Justify your answer.
Daljeet: During a decomposition reaction, a substance decomposes to give two simpler compounds. \(\mathrm{MgCO_3}\) decomposes on heating to magnesium oxide and carbon dioxide.
Avik: No, during a decomposition reaction, a substance decomposes to give two elements. Water on electrolysis gives hydrogen and oxygen, both are elements.
II. Analyse the observations given in following two cases. Are these observations correct? Give reasons to support your answer.
(i) Iron fillings are added to an aqueous solution of magnesium sulphate.
Observation: The colourless solution turns greenish due to formation of iron sulphate.
(ii) Aluminium metal is added to dilute sulphuric acid
Observation: Brisk effervescence are seen due to evolution of a gas.

An organic compound "X" with formula \(\mathrm{C_2H_6O}\) is used to blend with petrol in order to reduce the dependence on fossil fuels and lower down the harmful emissions from the cars. It is also used as a solvent in medicines such as tincture iodine, cough syrups and many tonics.
(i) Draw the electron dot structure of "X".
(ii) Write the name and formula of the next homologue of "X".
(iii) Write the reaction of "X" with acetic acid to form a sweet smelling substance.

Carbon forms millions of compounds whereas silicon, which is just below it in the Periodic Table, forms a few compounds. Explain the reason for the difference in their ability to form compounds.