Test: Chemical Reactions & Equations - 4 - RRB Group D / RPF Constable MCQ

When calcium oxide (chemical formula: Ca0) reacts with water (chemical formula: H20), the following reaction takes place:

The product of this reaction is calcium hydroxide, also known as slaked lime. Thus, when calcium oxide reacts with water, slaked lime is produced. 
 

Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. Both metals and non-metals take part in displacement reactions.

This is due to the Thermal decomposition reaction in which reactants decomposes to form products.

This is an example of a Redox reaction in which both the oxidation and reduction take place simultaneously.

In option (1) , if oxygen is highly combustible then it catch fire. Then how do we live, moreover hydrogen is a combustible substance. In option (2) hydrogen is a combustible substance but not oxygen. In option ( 3) oxygen is the supporter of fire but not the hydrogen.

Aluminium, zinc and iron are more reactive than copper therefore displaces from its solution.

PbSO₄ - Lead (II) Sulfate

Water (H₂O) contains two parts hydrogen and one part oxygen. Therefore, the amount of hydrogen and oxygen produced during electrolysis of water is in a 2:1 ratio. During electrolysis, since hydrogen goes to one test tube and oxygen goes to another, the amount of gas collected in one of the test tubes is double of the amount collected in the other.

Fats and oils in food kept for a long time get oxidized and become rancid and the taste of food changes and cause infection on eating. This is called rancidity

Hydrogen gas and iron chloride are produced.
Fe + HCl --> FeCl₂ + H₂

When an iron nail dipped in the copper sulphate solution than iron displaces copper from the copper sulphate because iron is more reactive than copper. Therefore the colour of the copper sulphate solution changes.
The reaction involved is

The reaction is represented as follows:
2AgNO₃ + Cu --------> Cu(NO₃)₂ + 2Ag ↓
Observation: Clear solution of AgNO₃ turns Blue
Type: Single displacement reaction

The given equation is a displacement reaction in which Fe of Fe₂O₃ has been displaced by Al. Hence, (b) is the correct answer.

A double displacement reaction, also known as a double replacement reaction or metathesis, is a type of chemical reaction where two compounds react, and the positive ions (cation) and the negative ions (anion) of the two reactants switch places, forming two new compounds or products. 

In copper sulphate as iron is more reactive than copper.

Chemically, rust is hydrated ferric oxide (Fe₂O₃.nH₂O)

The displacement reaction that occurs is Zn(s)+ CuSO₄(aq) → ZnSO₄(aq)+Cu(s) (Brownish black)  

Explanation: When Zinc is treated with dilute HCl, zinc being more reactive than hydrogen displaces hydrogen from its salt solution and thus produce zinc chloride and hydrogen gas.

This is a single replacement reaction as more reactive zinc displaces hydrogen. the hydrogen gas is odorless and colorless and burns with a pop sound when a burning match stick is brought near it.

A precipitation reaction occurs. Yellow precipitates of lead iodide are formed.
The equation for this reaction is Pb(NO₃)₂ + 2KI -----> PbI₂ + 2KNO₃.

Oxidation is  loss of electrons. Reduction is gain of electrons. Reducing agents are the electron losing species. Oxidizing agents are electron accepting species.

Rusting of iron is a chemical change. Dissolution of sugar or salt in water is a physical change. In exothermic reaction energy is released. In endothermic reaction energy is absorbed. 

Reduction is the gain of hydrogen.. Oxidation is the loss of hydrogen. 
Rancidity is the unpleasant taste and foul smell in fatty food. 
Corrosion is eating away of metal in the presence of air and moisture. 

Evolution of gas is a chemical change. According to the law of conservation of mass , mass of reactant is equal to mass of products. Increase in temperature is exothermic change. Evolution of hydrogen gas causes a pop sound.