Answer :

(i) XeF2 undergoes hydrolysis


Since xenon is a noble gas it has a stable configuration in its natural state so it would undergo reduction to achieve stability, leading to formation of hydrofluoric acid.



The release of O2 and HF production is exothermic and tends to release high amount of heat during the reaction. (Balancing does not require brainstorming as it is simple redox reaction)


(ii) MnO2 is heated with conc. HCl


The above reaction is a redox reaction which can be solved by using methods of oxidation number in acidic medium



Step (i) we generate the unbalanced skeleton:



Step (ii) Identify which reactants are oxidized and reduced, and write the half-cell reaction for them along with the electron transfers carefully make equal number of atoms of reduced and oxidized redox couples.


Oxidation:


Reduction:


Step (iii) Balance the number of atoms of reduced and oxidized redox couples. Here in reduction reaction Cl is also required to be balanced present in acidic condition, we had HCl molecule on LHS of reduction reaction.


Oxidation:


Reduction:


Step (iv) For acidic solutions, balance the charge by adding H+ on required side of the equation.


Oxidation:


Reduction:


Step (v) Balance the oxygen atoms. There are 2 oxygen atoms in reduction reaction, so add 2 water molecule to RHS of the equation to balance oxygen.


Oxidation:


Reduction:


Step (vi) Make the electron lost and gain equal in both oxidation and reduction reaction. Since here the electron lost and gain are same the reaction remains unchanged.


Oxidation:


Reduction:


Step (vii) Combine these two equations by adding them so that all reactants and products remain in the same side.



Step (viii) Simplify the equation by eliminating similar terms on both sides of equation.



The charge on both sides is 0, thus reaction is balanced.


OR


(i) - increasing acidic character


Acidic character is dependent on the ease with which the species can donate proton atom or accept electron. Here the said compounds are hydrides of group 16. Thus the ease with which the atoms can give the proton is more acidic.


Establishing this fact, we know that as the atomic size increases the nuclear attraction is significantly reduced due shielding effect of d & f-orbitals and increasing atomic size.


This increases the covalence of the bond and becomes easier to donate that proton. As we move down the group the atomic size increases and thus decreases charge density over the central atom which then helps in the proton donation.


Thus the increasing order of acidic nature is:



(iii) - decreasing bond enthalpy


As we move down in a group in the periodic table, the atomic size increases. This increase in atomic size thus in turn increases the bond length of the corresponding hydrogen halides in case of halogen group.


Bond length and its strength is inversely proportional to the nuclear attraction, and as the atomic size increases the nuclear attraction decreases (nuclear attraction also decrease due to shielding effect) which increases the bond size and decreases bond strength.


Thus the decreasing order of bond strength would be in order of increasing bond length:



The bond enthalpy is the energy required to break a bond between two atoms, thus the same order applies to decreasing bond enthalpy.


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