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When a covalent bond breaks, under the influence of incoming electrophile or nucleophile,  it happens in two ways

1.Heterolytic fission 

2.Homolytic fission 

Homolytic fission : when a covalent bond breaks,  the two electrons of bond are equally divided between two atom forming bond. The new species formed both carries single unpaired electron and are called free radicals. 

Heterolytic fission : when a covalent bond breaks, two electrons of bond are unequally divided among atom of compound. One atom get both electrons and become negatively charged, called nucleophile. Other atom which do not get any electron get positively charged and called electrophile. 

What are the common physical and chemical features of alkali metals? read less

Heavy Water is used as a primary coolant to transport heat generated by the fission reaction to secondary coolant, light water. The light water takes the heat energy from Heavy Water and generates steam at an appropriate pressure for running steam turbines. Steam turbines drive generators to generate Electricity.

−1H2O2⟶−2H2O+0O2

H ₂O ₂ is unstable under alkaline conditions. Decomposition is catalysed by various redox-active ions or compounds, including most transition metals and their compounds (e.g. manganese dioxide ( MnO ₂), silver, and platinum).

Temporary Hardness: Caused by bicarbonates of calcium and magnesium. This hardness can be easily removed by boiling, as the bicarbonates decompose to insoluble carbonates that can be filtered out.

Permanent Hardness: A tougher nut to crack, arising from chlorides and sulfates of calcium and magnesium.

A Conc. H2SO4 cannot be used because it acts as oxidizing agent also and gets reduced to SO2. Zn + dil H2SO → ZnSO4 + 2H2O + SO2 b Pure Zn is not used because it is non-porous and reaction will be slow. The impurities in Zn help in constitute of electrochemical couple and speed up reaction.