(i) Conc. HNO3 has no effect on Al i.e., Al is rendered passive by nitric acid. This is due to surface oxidation and formation of a thin film of oxide on its surface which prevents further reaction. So, an acid can be stored in aluminium container.
(ii) Aluminium reacts with sodium hydroxide in water to produce hydrogen gas. The bubbles of hydrogen gas help to agitate the mixture, helping to dislodge the clog.
2Al+2NaOH+2H2O → 2NaAlO2+3H2 ↑
(iii) Graphite is used as a dry lubricant in machines running at high temperature because of its soft and greasy nature. This is due to its layered structure, adjacent layers can easily slide over each other and therefore, it is very soft and slippery.
(iv) Diamond is used as an abrasive because of its hard nature. It is very difficult to break its extended covalent bonding and therefore, diamond is the hardest natural substance on the earth.
(v) Alloys of aluminium ; Magnalium and Duralumin both of which contain about 95% of the metal, are used for making aircraft body because these are light and tough.
(vi) Although the metal as such is not affected by water, but when kept overnight it may be slowly affected by moisture in the presence of oxygen (air) to give Al2O3.Al2O3 may dissolve in water as Al3+ ions which are injurious to health.
(vii) The metal is not affected by air and moisture and also because of its good conductivity, it is used to make transmission cables.