The comfortable distance to read objects is 25 cm. Some persons can see objects close to them clearly, but cannot see distant objects so clearly. On the other hand some persons can not see objects close by clearly but they can see distant objects quite well. These are called Myopia and Hypermetropia respectively.

(i) This 'pop-up' sound indicates the presence of hydrogen gas.
(ii) We conclude that metal reacts with sodium hydroxide to produce hydrogen gas.

Yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of gas fill the dough and increase its volume. This is the basis of the use of yeast in baking industry.

1. (C) Water, (F) Blue.
2. (B)Non-metallic oxide, (F) Red

Light travels fastest in vacuum than any other medium because there is no obstruction to the passage of light in vacuum.

Kaleidoscope is a device that is generally used by the designers of wallpapers and fabrics.

Since rods are sensitive to dim light whereas cones are sensitive to the bright light.

Zinc is most reactive among three and copper is least reactive among three. Reactivity of iron is in between zinc and copper.

The given observation means that heat is transmitted from one end to the other. This property of metals is called conductivity.

Rhizobium bacteria commonly live in the root nodules of leguminous plants.

Bacillus anthracis causes of anthrax.

(a) Z is a Protozoa
(b) Y is Anopheles mosquito. It is a female.
(c) Preventive measure: Use mosquito nets and repellents.

a) Chemical properties of metals:
(i) Metals react with oxygen to produce oxides which are alkaline in nature. e.g.,
\(\underset{Magnesium}{Mg}+\underset{Oxygen}{O_2}⟶\underset{Magnesium\ oxide}{2MgO}\)
(ii) Metallic oxides produce bases by reacting with water differently
\(\underset{Sodium\ oxide}{Na_2O}+\underset{Water}{H_2O}⟶\underset{Sodium\ hydroxide}{2NaOH}\)
(iii) Metals react with acid to produce hydrogen gas
\(\underset{Hydrochloric\ acid}{2HCI}+\underset{Sodium}{2Na}⟶\underset{Sodium\ chloride}{2NaCl}+\underset{Hydrogen}{H_2}\)
(iv) More reactive metals displace the less reactive metals from their compounds in an aqueous solution 
\(\underset{Copper\ Sulpahte}{CuSO_4}+\underset{Zinc}{Zn}⟶\underset{Zinc\ Sulphate}{ZnSO_4}+\underset{Copper}{Cu}\)
(b) Chemical properties of Non-metals
(i) Non-metals react with oxygen to produce oxides which are acidic in nature
\(\underset{Sulphur}{S}+\underset{Oxygen}{O_2}⟶\underset{Sulphur\ dioxide}{SO_2}\)
\(\underset{Sulphur\ dioxide}{SO_2}+\underset{Water}{H_2O}⟶\underset{Sulphurous\ Acid}{H_2SO_3}\)
(ii) Non-metals do not react with water.
(iii) Non-metals do not show displacement reactions.