ZnS forms soluble complex Na₂ ​[Zn(CN)₄​] while PbS forms froth.
When the minerals are expected to contain PbS and ZnS, suitable depressants such as NaCN are added.
The added NaCN, selectively prevents ZnS from coming to the froth by forming soluble complex Na₂​[Zn(CN)_4​] and PbS is removed along with the froth.

Earlier rate R = K[A]ⁿ [B]^m
Now rate R₁ = K[2A]ⁿ [B/2]^m
R₁/R = 2^n-m

The hypersensitivity of some persons towards certain drugs (penicillin, sulpha drugs), dust, pollen grains, cat fur, a particular food or fabric, etc. is called allergy. Allergy is caused by release of a substance called histamine in the body Antihistamines are drugs which either reduce or inhibit the action of histamine in the body thereby preventing allergy. Two important antihistamine or anti-allergic drugs are brompheniramine and terfenadine. .
Mode of action. Histamines interact with the binding sites of receptor in the body to produce allergy. Antihistamines compete with histamines for these binding sites of receptor and thus do not allow histamine to produce allergy. Thus, antihistamines are drugs which interfere with the natural action of histamine by competing for histamine binding sites of receptor.

Alitame is a high potency artificial sweetener. Therefore, it is difficult to control the sweetness of the food to which it is added.

(a) N does not have d-oribitals to accommodate the electrons donated by O of  \({ H }_{ 2 }O\), therefore, attack of \({ H }_{ 2 }O\) occurs on the CI atom which has d- orbitals to accommodate the extra electrons donated by \({ H }_{ 2 }O\). Consequently Cl-O bond is formed leading to the formation of HOCl and NH₃ as shown below:

In contrast, both P and CI have d-orbitals to accommodate electrons donated by \({ H }_{ 2 }O\). But P-O bond is much stronger than CI-O bond. As a result, attack of \({ H }_{ 2 }O\) molecules occurs preferentially on P of PCI₃ to form H₃PO₃ and HCl.

(b) The basic character of SOCI₂ is due to the presence of a lone pair of electrons on the S-atom. Further, in SOCI₂, S also has empty d- orbitals which can be used to accept electrons. Therefore, SOCI₂ also behaves as a Lewis acid.
 

ZnCl₂ combines with the NH₃ produced to form the complex salt [Zn(NH₃)₂ Cl₂] as otherwise the pressure developed due to NH₃ would crack the seal of the cell.

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