Answer: The correct answer is option B.
Explanation: Reactivity of elements is defined as the tendency to loose or gain electrons.
These reactions are a type of single displacement reactions. A single displacement reaction is a type of reaction in which an element displaces another element in a chemical reaction. These are studied with the help of reactivity series.
The element which lies above in the reactivity series can easily displace the element which lies below in the reactivity series.
Option A: This reaction will not yield a stable product because Zinc lies below Aluminium in the reactivity series.

Option B: This reaction will yield a stable product because Sodium lies above Calcium in the reactivity series.

Option C: This reaction will not yield a stable product because Hydrogen lies below Magnesium in the reactivity series.

Option D: This reaction will not yield a stable product because Calcium lies below Barium in the reactivity series.

Option E: This reaction will not yield a stable product because barium lies below Lithium in the reactivity series.

Answer:

Explanation:
Given that,
Initial volume, 
The pressure changes from 73.2 kPa to 122.5 k.Pa.
We need to find the new volume occupied by the air. Let it is V₂. It can be calculated using Boyle's law such that,

So, the new volume is
.
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Answer:
Mass = 2.12 g
Explanation:
Given data:
Volume of KMnO₄ = 255 mL (255/1000 = 0.255 L)
Molarity = 0.0525 M
Mass in gram = ?
Solution:
First of all we will calculate the number of moles.
<em>Molarity = number of moles of solute / volume in litter</em>
0.0525 M = number of moles of solute / 0.255 L
Number of moles of solute = 0.0525 M ×0.255 L
Number of moles of solute = 0.0134 mol
Mass in gram:
<em>Number of moles = mass/ molar mass</em>
Mass = moles × molar mass
Mass = 0.0134 mol × 158.04 g/mol
Mass = 2.12 g