Which pair of oxides is acidic in nature?
(a) B2O3, CaO
(b) B2O3, SiO2
(c) N2O, BaO
(d) CaO, SiO2

Q: Why is $N_2O$ neutral and not acidic if Nitrogen is a non-metal?

While it's a general rule that non-metal oxides are acidic, $N_2O$ (along with $NO$ and $CO$) is an exception. It does not react with water to form an acid, nor does it react with bases to form a salt. Its specific molecular structure and bonding do not facilitate the acceptance of electron pairs or the release of protons.

Q: Is $SiO_2$ really acidic? Isn't it just sand?

Yes, $SiO_2$ is indeed acidic! While it is highly unreactive at room temperature (which is why sand doesn't dissolve in the ocean), it will react with strong bases like $NaOH$ or $KOH$ at elevated temperatures to form silicates. This reaction with a base proves its acidic nature.

Q: What about amphoteric oxides? Where do they fit in?

Amphoteric oxides sit right on the borderline between metals and non-metals. Elements like Aluminum ($Al_2O_3$), Zinc ($ZnO$), and Lead ($PbO$) form oxides that can react with BOTH acids and bases. They are the 'chameleons' of the oxide world.

Q: How can I easily remember which oxides are neutral?

There are only three common neutral oxides you need to memorize for JEE/NEET: Carbon monoxide ($CO$), Nitric oxide ($NO$), and Nitrous oxide ($N_2O$). Just remember this trio, and assume other non-metal oxides are acidic.

Q: Why does $B_2O_3$ act as an acid?

Boron is an electron-deficient element (it only has 3 valence electrons). In $B_2O_3$, the boron atoms are eager to accept a pair of electrons to complete their octet. This makes $B_2O_3$ a classic Lewis acid, allowing it to react readily with bases.

Question

Which pair of oxides is acidic in nature?

Options:

(A) $	ext{B}_2	ext{O}_3, 	ext{CaO}$

(B) $	ext{B}_2	ext{O}_3, 	ext{SiO}_2$

(C) $	ext{N}_2	ext{O}, 	ext{BaO}$

(D) $	ext{CaO}, 	ext{SiO}_2$

Sigma Percentile · Accepted Answer

### The Periodic Dance of Oxides

Imagine you are taking a stroll across the modern periodic table. As you walk from the far left to the right, you are not just passing by different elements; you are witnessing a profound shift in chemical personality. On the extreme left, you meet the highly electropositive alkali and alkaline earth metals. These elements love to give away electrons. When they bond with oxygen, they form ionic lattices. If you drop these metal oxides into water, they eagerly grab protons from water molecules, releasing hydroxide ions ($OH^-$). This is why metal oxides like $CaO$ and $BaO$ are fundamentally **basic in nature**.

### Crossing the Metalloid Line

As you continue your journey towards the right side of the periodic table, the elements become more electronegative. They hold onto their electrons tightly. When non-metals like Boron ($B$) and Silicon ($Si$) bond with oxygen, the bonds are highly covalent. These non-metal oxides are electron-deficient or have highly polarized bonds. When they encounter water (or a base), they act as electron-pair acceptors (Lewis acids). Therefore, oxides like $B_2O_3$ and $SiO_2$ are **acidic in nature**.

### The Ultimate Chemical Test

How do we prove that an oxide is acidic? We throw it into a battle with a strong base! If it reacts to form a salt and water, it has proven its acidic identity. Let's test our candidates:

When Boron trioxide reacts with Sodium Hydroxide, it forms Sodium Metaborate:
$$B_2O_3 + 2NaOH \longrightarrow 2NaBO_2 + H_2O$$

Similarly, Silicon dioxide (which is essentially sand) might seem inert, but at high temperatures, it reacts with Sodium Hydroxide to form Sodium Silicate:
$$SiO_2 + 2NaOH \longrightarrow Na_2SiO_3 + H_2O$$

Both reactions perfectly demonstrate the acidic character of $B_2O_3$ and $SiO_2$.

### The Neutral Traps

Now, you might look at Nitrogen and think, "Aha! Nitrogen is a non-metal, so its oxide $N_2O$ must be acidic!" **Stop right there.** This is a classic trap set by examiners. While most non-metal oxides are acidic, there is a famous trio of exceptions: **$CO$, $NO$, and $N_2O$**. These three are **neutral oxides**. They do not react with acids or bases to form salts.

By carefully analyzing the periodic position and remembering the neutral exceptions, we can confidently conclude that the only pair consisting entirely of acidic oxides is $B_2O_3$ and $SiO_2$.

Animated Solution for Chemistry - Periodicity in Properties: Which pair of oxides is acidic in nature?

Select Answer:

Visualized Solution

$Nature of Oxides$

$Analyzing Ca and Ba$

$The Neutral Exception$

$Analyzing B and Si$

$Chemical Proof$

$Conclusion$

The Sigma Insight: Periodic Table and Periodic Properties

The Periodic Dance of Oxides

Crossing the Metalloid Line

The Ultimate Chemical Test

The Neutral Traps

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