Four students A, B, C and D did their experiment of finding the focal length of convex lens by obtaining image of a distant object as follows:

• Student A used the window grill in the laboratory as the object and a white paper sheet held in hand as the screen.

• Student B used a distant tree in the shade and a white thick held in a stand as the screen.

• Student C used a well illuminated laboratory window grill as the object and a white paper sheet held in a stand as the screen.

• Student D used a well illuminated distant tree as the object and a white thick board held in a stand as the screen.

Which student has used the correct method for performing experiment out of the above setups?

Vishakha carried out saponification reaction in the lab and she gave following comments as:

(i) Soap is salt of fatty acid.

(ii) Heat is absorbed in this reaction.

(iii) Reaction mixture is basic in nature

(iv) These are neutralization reaction

The correct statements are:

Select from the following salts which may be used to prepare hard water required for the experiment.

A. CaSO₄

B. Na₂SO₄

C. CaCl₂

D. K₂SO₄

E. NaHCO₃

F. MgCl₂

In the setup shown below, a clear image of a distant object is obtained on the screen. The focal length of the concave mirror is:

In the experiment on refraction of light through a rectangular glass slab done by four students A, B, C and D, the following observations were made:

(a) The emergent ray moves towards the normal after second refraction through glass slab with i = e

(b) The emergent ray moves away from the normal after second refraction through glass slab ∠ i < ∠e

(c) For any angle of incidence, always ∠I ˃ ∠e, always.

(d) The emergent ray moves away from normal after second refraction through glass slab with ∠i = ∠e

The student who has made the correct observation is: