Chemical Reactions & Equations - 3 - Class 10 MCQ

Silver chloride turns grey due to the formation of silver by decomposition of silver chloride.

Combination reactions are those in which two or more reactants react to give one product only.

When a solution of potassium iodide is added to a solution of lead nitrate taken in a test tube, the precipitation of a yellowish solid is observed. This yellowish solid is lead iodide. Potassium nitrate is formed along with lead iodide.
This is an example of double displacement reaction.
Also , as yellow precipitate is formed , this is also an example of precipitation reaction

Balanced Equation: Pb(NO₃)₂ + 2KI → 2KNO₃ + PbI₂

In the given reaction, there is an exchange of ions between the reactants, thus it is a double displacement reaction. Also, white precipitate of barium sulphate is formed as a product, thus it is also an example of precipitation reaction.

Option (i) is correct as iron(Fe) is combining with oxygen to form iron(II,III) oxide(Fe2​O3​).
Option (ii) is correct as water(H2​O) is being reduced by removal of oxygen to form hydrogen (H2​) gas.
Option (iv) is correct as water(H2​O) itself is being reduced and is oxidising Iron(Fe), thereby acting as an oxidising agent.

A decomposition reaction occurs when an energy is supplied to a compound causing it to decompose (break down) into multiple different chemical substances.

But in 'C' it is a combination reaction

The formula of ammonium phosphate is 
( NH₄) ₃ PO₄ . The salt compound consists of positively charged ammonium cations and phosphate anion which carries -3  formal charge.

Mg is more reactive than Zn. So Zn cannot displace Mg. Therefore,option C is the answer.

Oxidation process involves :-
Addition of O₂ or electronegative element. 
Removal of H/ Electropositive element. 
Loss of electron.

Lead sulphate being insoluble will not dissociate to give lead ions. Hence precipitation of lead iodide will not be possible with lead sulphate.

Lead acetate is a colourless compound. On coming in contact with potassium iodide crystal, the formation of lead iodide occurs that is bright yellow in colour.  Also, other salts, ammonium nitrate and potassium sulphate do not possess the lead ion, therefore lead iodide can not be formed using them.