Equipment containing mercury should be handled carefully.
If broken or discarded, their disposal should be done carefully.
Associated Value: The learners will handle and dispose such poisonous items more carefully.

Calcium starts floating because the bubbles of hydrogen gas formed sticks to the surface of the metal.
Ca + 2H₂O \(\rightarrow \) Ca(OH)₂ + H₂

The two metals are:
(i) Calcium (Ca)
(ii) Magnesium (Mg)
They start floating because the bubbles of hydrogen gas which are formed during the reaction stick to the surface of the metal.

Since an oxide of element is acidic in nature. therefore, the element  A will be a non-metal

Metals low in activity series can be obtained by reducing their sulphides or oxides by heating. Mercury is the only metal that exists as liquid at room temperature. It can be obtained by heating cinnabar (HgS), the sulphide ore of mercury. The reactions are follows:
\(2HgS+{ 3O }_{ 2 }\underrightarrow { Heat } 2HgO+{ 2SO }_{ 2 }\\ \quad \quad \quad 2HgO\underrightarrow { Heat } 2Hg+{ O }_{ 2 }\)

It is because HNO₃ is a strong oxidising agent. It oxidises the H₂ produced to H₂O.

(i) Metals conduct electricity because they have electrons which are free to move. They offer little resistance to the flow of current. Silver and copper are the best conductors of electricity.
(ii) Reaction of metals with nitric acid does not evolve hydrogen gas; it is because HNO₃ is a strong oxidizing agent. It oxidises H₂ produced to water and is itself reduced to any of its oxides such as N₂O, NO or NO₂.
(iii) Pure gold is 24 carat and is very soft. Therefore it is not suitable for making jewellery. It is alloyed with Cu or Ag to make it hard. Generally 22 carat gold is used for making ornaments, which contains 22 parts pure gold and 2 parts of either Cu or Ag. 

Most of the metal sulphides are insoluble in water whereas metal halides are generally soluble. The metal halides (NaCl, MgCl₂) are washed away with rain or river water in dissolved state and so the halide ores occur in lakes and seas.

The metallic oxides which show the properties of acids as well as bases are called amphoteric oxides. It means that they react with both bases and acids to form salt and water.
e.g. ZnO and Al₂O₃
ZnO(s)                         +   2HCl(aq)            \(\rightarrow\) ZnCl₂ (aq)    + H₂O(l)
Zinc oxide (As a base) Hydrochloric acid      Zinc chloride    Water
ZnO(s)                         + 2NaOH(aq)            \(\rightarrow\) Na₂ZnO₂(aq) + H₂O(l)
Zinc oxide (As an acid)  Sodium hydroxide      Sodium zincare   Water

Metal is obtained from its oxide by reduction. This reduction can be done either by heating with carbon (coke) or by using highly reactive metals such as sodium, calcium, aluminium etc.
e.g. ZnO(s) + C(s) \(\rightarrow\) Zn(s) + CO(g)
 Zinc oxide    Coke     Zinc   Carbon monoxide
This reaction is highly exothermic. The heat produced is so large that metal is produced in the molten form.

Zinc being more reactive than iron displaces iron from iron (II) sulphate solution. Thus, the green colour of the solution fades and iron metal gets deposited.
Zn(s) + FeSO₄ (aq)  \(\rightarrow\) ZnSO₄ (aq)  + Fe (s)
Zinc      (Green)              (Colourless)   Iron (Deposited)
 

Malleable A substance or material, which can be beaten into thin sheets is called malleable, e.g. metals like Ag (silver), Au (gold) etc.
Ductile A substance capable of being drawn into thin wires is called ductile, e.g, metals like Ag, Au etc.

A layer of basic copper carbonate is formed by the reaction of air on copper metal.
This layer being insoluble in water, cannot be cleaned with water alone. But, it is soluble in acids so lemon containing citric acid, tamarind containing tartaric acid or any other sour substance containing acid can be effective in cleaning the vessels. As these acids neutralises the basic copper carbonate and dissolves the layer. Hence, surface of copper vessels are cleaned with lemon or tamarind juice to give its characteristics lustre.