Heavy atoms such as gold, platinum have nucleus. Heavy nucleus contains large amount of positive charge. When a beam of \(\alpha \)-particles is shot at a thin gold foil, most of them pass through without much effect.
Some however, are deflected back or by small angles due to enormous repulsive force of heavy nucleus. If light aluminium foil is used, the number of \(\alpha \) -particles deflected back or those deflected by small angles will be negligible.

Nucleus of Li atom has 3 protons and 4 neutrons.
Charge on one proton =1.60 x 10^-19 coulombs
Charge on 3 protons (i.e. charge on nucleus)
= \(3\times 1.60\times 10^{ -19 }C=4.80\times 10^{ -19 }C\)
Mass of proton mass of neutron \(\simeq 1.67\times 10^{ -27 }kg\) 
Mass of nucleus = \(7\times 1.67\times 10^{ -27 }kg\)
= \(11.69\times 10^{ -27 }kg\)

Aluminium \(([Ne]^{ 3{ s }^{ 2 } } \ 3p'\) can achien the electronic configuration of the nearest noble gas (Ne) by losing only three electrons, Al³⁺ = 1s²2s²2p⁶ . Aluminium with not form the Al⁴⁺ ion because an extremely high amount of energy would be required to remove an electron from the stable noble gas configuration.

There is greater intermolecular hydrogen bonding in H₂ O than that in HF as each H₂ O molecule forms four H-bonds with water molecules,, whereas HF forms only H-bonds with other HF molecules. Greater the intermolecular H-bonding, greater is the viscosity. Hence, HF is less viscous than  H₂ O

In gaseous state at high temperature,  BeCl₂ exists as linear molecule Cl-Be-Cl, thus the hybridisation of the central atoms is sp  

In solid state,it has a polymeric structure with chlorine bridges as follows

Two Cl-atoms are listed to be atom by two coordination bonus and two by covalent bonds. For these bonds to be formed, Be in the excited state with the configuration undergoes Sp³ hybridization. Two half-filled hybrid orbitals will form normal covalent bonds with two Cl-atoms. The other two Cl-atoms are coordinated to Be-atom. The other two Cl-atoms are coordinated be Be-atom by donating electron pairs into the empty hybrid orbitals.

A substance has a perfectly ordered arrangement of its constituent particles only at absolute zero. Hence, entropy is zero only at absolute zero. Enthalpy of formation is the heat change involved in the formation of one mole of the substance from its elements. An element formed from itself means no heat change, i.e \(\Delta _{ f }H^{ \circ }=0\) .

\(G=H-TS,\quad G_{ 1 }=H_{ 1 }-TS_{ 1 },{ G }_{ 2 }=H_{ 2 }-TS_{ 2 }\)
\( G_{ 2 }-G_{ 1 }=H_{ 2 }-H_{ 1 }-T({ S }_{ 2 }-S_{ 1 })\)
\( \Delta G=\Delta H-T\Delta S\)
\( \Delta S_{ total }=\Delta S_{ sys }+\Delta S_{ sure }\)
\( \Rightarrow \Delta S_{ total }=\Delta S_{ sys }-\frac { q }{ T } \)
\( \Rightarrow T\Delta S_{ total }=T\Delta S_{ sys }-q=T\Delta S_{ sys }-\Delta H\)
\(T\Delta S_{ total }=-\Delta G\Rightarrow \Delta G=-T\Delta S_{ total }\)

\(\Delta H=hydration \ energy-lattice \ energy\)
\(\Delta H=-774.1kJmol^{ -1 }-(-777.8kJmol^{ -1 })=3.7kJmol^{ -1 }\)
\(\Delta G=-9.11kJmol^{ -1 }\)

Al reacts with conc. HNO₃ to form a protective layer of aluminium oxide on its surface which prevents it from further reaction.
\(2Al(s)+6HNO_{ 3 }(conc.)\rightarrow Al_{ 2 }O_{ 3 }(s)+6NO_{ 2 }(g)+3H_{ 2 }O(l)\)
                                         Alumina (a passive protective layer)
Therefore, Al becomes passive that's why aluminium containers can be used to transport conc.HNO₃.

NaOH reacts with Al to evolve dihydrogen gas. The pressure of the hydrogen gas can be used to open drains.
2Al(s) + 2NaOH(aq) + 2H₂O(l) \(\rightarrow \) 2NaAlO₂(aq) + 2H₂(g)