Question

Which of the following cations below will show borax bead blue in oxidizing flame?
A.$F{e^{3 + }}$
B.$F{e^{2 + }}$
C.$C{o^{2 + }}$
D.$C{u^{2 + }}$

Answer 1

Hint:
We will first define what are cations and anions along with examples and properties. Then we will explain what is an oxidizing flame. Further we will learn about borax beads, its structure and properties.

Complete step by step answer:
-Cations: When an atom loses an electron there is a positive charge on it. This ion which is positively charged is known as a cation.
Now we will see some properties of cations as follows:
-Mostly cations are metals.
-It has more number of protons than electrons.
-During electrolysis it gets attracted towards cathode.
Examples of cations: $A{l^{3 + }},B{a^{2 + }},C{a^{2 + }},C{o^{2 + }},C{u^{2 + }},F{e^{2 + }},F{e^{3 + }},N{i^{2 + }},{K^ + },N{a^ + },Z{n^{2 + }}$ .
-Anions: When the atom gains an electron there is a charge which is negative. This negatively charged ion is said to be an anion.
Properties of anions are given below:
-Most of the anions are non metals.
-It consists of more electrons than the number of protons.
-During electrolysis it gets attracted to the anode.
Examples of anions: $C{l^ - },B{r^ - },{I^ - },{F^ - },{S^{2 - }}$ .
-Oxidizing flame
-The flame or a part of it consisting of excess oxygen is known as oxidizing flame.
-The color of the flame is blue.

-Borax bead:
-It is a mixture of sodium metaborate and boric oxide.
-These borax beads are used in order to detect radicals, hence its test is known as borax bead test.
-In the borax bead test, the cations that change its color blue in oxidizing flame are $C{o^{2 + }}$ and $C{u^{2 + }}$ .
So the correct answer is option c) $C{o^{2 + }}$ and option d) $C{u^{2 + }}$ .

Note: In reducing flame, $C{o^{2 + }}$ does not change its color, it remains blue. Whereas the color of $C{u^{2 + }}$ changes into red-brown or colorless.