JEE Main 2026 — Chemistry Inorganic Chemistry

2026mcqmedium

Among $Fe^{2+}, Fe^{3+}, Cr^{2+}$ and $Zn^{2+}$ , the ion that shows positive borax bead test and with highest ionisation enthalpy is:

Official previous-year question

Held on 2 Apr 2026 · Verified 6 Jul 2026.

Options

A
$Fe^{2+}$
B
$Zn^{2+}$
C
$Cr^{2+}$
D
$Fe^{3+}$

Did you get this right?

Solution

The borax bead test is given by transition metal ions that have unpaired electrons and form coloured compounds.

$Zn^{2+}$ has a completely filled $3d^{10}$ configuration, making it colourless, so it does not give a positive borax bead test.

The remaining ions and their electronic configurations are:

$Fe^{2+} : [Ar] 3d^{6}$

$Cr^{2+} : [Ar] 3d^{4}$

$Fe^{3+} : [Ar] 3d^{5}$

The ionisation enthalpy of an ion refers to the energy required to remove an electron from it. $Fe^{3+}$ has a highly stable half-filled $d$ -subshell configuration ( $3d^{5}$ ). Removing an electron from this stable configuration requires significantly more energy compared to removing an electron from $Fe^{2+}$ ( $3d^{6}$ ) or $Cr^{2+}$ ( $3d^{4}$ ).

Therefore, $Fe^{3+}$ shows a positive borax bead test and has the highest ionisation enthalpy among the given ions.

Answer: $Fe^{3+}$

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JEE Main Inorganic Chemistry in other years

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JEE Main 2026 — Chemistry Inorganic Chemistry

2026mcqmedium

Among $Fe^{2+}, Fe^{3+}, Cr^{2+}$ and $Zn^{2+}$ , the ion that shows positive borax bead test and with highest ionisation enthalpy is:

Official previous-year question

Held on 2 Apr 2026 · Verified 6 Jul 2026.

Options

A
$Fe^{2+}$
B
$Zn^{2+}$
C
$Cr^{2+}$
D
$Fe^{3+}$

Did you get this right?

Solution

The borax bead test is given by transition metal ions that have unpaired electrons and form coloured compounds.

$Zn^{2+}$ has a completely filled $3d^{10}$ configuration, making it colourless, so it does not give a positive borax bead test.

The remaining ions and their electronic configurations are:

$Fe^{2+} : [Ar] 3d^{6}$

$Cr^{2+} : [Ar] 3d^{4}$

$Fe^{3+} : [Ar] 3d^{5}$

Therefore, $Fe^{3+}$ shows a positive borax bead test and has the highest ionisation enthalpy among the given ions.

Answer: $Fe^{3+}$

Your note

JEE Main Inorganic Chemistry in other years

Keep practicing Inorganic Chemistry

Work through every JEE Main Inorganic Chemistry PYQ, year by year.

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JEE Main 2026 — Chemistry Inorganic Chemistry

Options

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Solution

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JEE Main Inorganic Chemistry in other years

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Physical Chemistry

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JEE Main 2026 — Chemistry Inorganic Chemistry

Options

Did you get this right?

Solution

Your note

JEE Main Inorganic Chemistry in other years

More JEE Main Inorganic Chemistry questions

Other Chemistry topics for JEE Main

Physical Chemistry

Organic Chemistry

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