$(a)$ State the reasons which lead to hypermetropia. With the help of suitable diagrams,explain this defect of vision and its correction.
$(b)$ Draw a diagram of an experimental arrangement for observing the scattering of light in a colloidal solution. Name the two chemicals used in this activity.

(N/A) Hypermetropia,also known as farsightedness,is a vision defect where a person can see distant objects clearly but cannot see nearby objects distinctly. This happens because the near point of the eye has shifted further away than the normal $25 \ cm$.
Reasons for hypermetropia:
$1$. The eyeball has become too short.
$2$. The focal length of the eye lens has become too large.
Correction: This defect is corrected by using a convex lens of suitable focal length,which converges the light rays before they enter the eye,allowing the image to form on the retina.
$(b)$ The experimental arrangement for observing the Tyndall effect (scattering of light) involves passing a strong beam of light through a colloidal solution (e.g.,sodium thiosulphate solution). The two chemicals used are:
$1$. Sodium thiosulphate $(Na_2S_2O_3)$
$2$. Concentrated sulphuric acid $(H_2SO_4)$