Conditions necessary for rusting of iron:
(i) Iron is exposed to moist air.
(ii) Presence of water droplets in the atmosphere.
(iii) Presence of Oxygen.

(i) Rust is the formation of scaling reddish brown hydrated ferric oxide on the surface of iron containing materials.
(ii) This compound is known as rust and the phenomenon of formation of rust in known as rusting.
(iii) \( 4 \mathrm{Fe}+3 \mathrm{O}_{2}+\mathrm{xH}_{2} \mathrm{O} \rightarrow 2 \mathrm{Fe}_{2} \mathrm{O}_{3} \cdot \mathrm{xH}_{2} \mathrm{O}\\ \quad \quad \quad \quad \quad\quad\text { (Rust hydrated ferric oxide) } \) 

(i) On heating 800^o C, aluminium burns very brightly forming its oxide.
(ii) 4 Al + 3 O₂ → 2 Al₂O₃ (Aluminium oxide)
(iii) A is Aluminium (Al)
(iv) B is Aluminium oxide (Al₂O₃)

(i) A - reddish brown metal - Copper
(ii) When copper is heated at < 1370 K in the presence of oxygen, copper forms black colour Copper (II) oxide (CuO).
(iii) \(2 \mathrm{Cu}+\mathrm{O}_{2} \stackrel{\text { below } 1370 \mathrm{~K}}{\longrightarrow} \underset{\text { (copper (Il)oxide-black) }}{2 \mathrm{CuO}}\)
(iv) When copper is heated at >1370 K in the presence of oxygen, copper forms red colour Cop-per (I) oxide \((\mathrm{Cu}_{2} \mathrm{O} )\)
(v) \(4 \mathrm{Cu}+\mathrm{O}_{2} \stackrel{\text { above } 1370 \mathrm{~K}}{\longrightarrow} \underset{\text { (copper-I-oxide-red) }}{2 \mathrm{Cu_2O}}\)
(vi) A - copper (Cu)
(vii) B - copper (II) oxide (CuO) - Black coloured
(viii) \(\mathbf{C} - copper-I-oxide \left(\mathrm{Cu}_{2} \mathbf{O}\right)-\operatorname{Red}\) coloured

Sodium

The process is froth floatation. Lighter sulphide, ores like zinc blende (ZnS).

It is the substance added to the ore to reduce the fusion temperature and to remove the impurities. E.g. Calcium oxide (basic), Silica (acidic).

Down the group, atomic size increases and hence the valence electrons are loosely bound. They require relatively less energy for the removal. Thus ionisation energy decreases down the group in periodic table

True. Noble gases show no tendency to accept electrons because the outer sand p orbitals of noble gases are completely filled. No more electron can be added to them and hence their electron affinities are zero

Atomic radii is defined as the distance from the centre of the nucleus of the ion upto the point where it exerts its influence on the electron cloud of the ion.

As move along the period, the shell number remains same but the number of protons increases. Increased positive charges impose strong attraction over electrons and thus the electron cloud shrinks towards the nucleus which results in decrease in atomic size.

d(C-C) = 1.54 A°
r(c) = \(\frac{d(c-c)}{2}\) = \(\frac{1.54}{2}\)
= 0.77A^o.

Properties such as atomic radius, ionic radius, ionization energy, electro negativity, electron affinity show a regular periodicity and hence they are called periodic properties.

(i) The main significance of modem periodic table is it gives a clear understanding of the general properties and trends within a group or a period.
(ii) To predict with accuracy the properties of any element.

The atoms of the group 18 elements have stable electronic configuration in their valence shells and hence they are unreactive.