List of top Science Questions asked in CBSE X

A spherical mirror and a thin spherical lens have each a focal length of −15 cm. The mirror and the lens are likely to be
Compare the power used in the 2 Ω resistor in each of the following circuits:
  1. a 6 V battery in series with 1 Ω and 2 Ω resistors,
  2. a 4 V battery in parallel with 12 Ω and 2 Ω resistors.
Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A?
An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image, its nature and size.
Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below -
I (amperes) 0.51.02.03.04.0
V (volts)1.63.4  6.710.213.2
Plot a graph between V and I and calculate the resistance of that resistor.
Fe2O3 + 2Al → Al2O3 + 2Fe 
The above reaction is an example of a:
An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focused image can be obtained? Find the size and the nature of the image.

What is hydrogenation? What is its industrial application?

Give reasons:
  1. Platinum, gold and silver are used to make jewellery.
  2. Sodium, potassium and lithium are stored under oil.
  3. Aluminium is a highly reactive metal, yet it is used to makeutensils for cooking.
  4. Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
What type of oxides are formed when non-metals combine with oxygen?
Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
How are involuntary actions and reflex actions different from each other?
How does chemical coordination occur in plants?
Which signals will get disrupted in case of a spinal cord injury?
Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
The brain is responsible for
The gap between two neurons is called a
Why do we apply paint on iron articles?
Which of the following is a plant hormone?
A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
What do you mean by a precipitation reaction? Explain by giving examples.
Name two metals which will displace hydrogen from dilute acids, and two metals which will not.