Amphoteric oxides are oxides that can react with both acids and bases to form salts and water. They have the ability to act as both acid and base depending on the conditions.

The amphoteric nature of an oxide depends on the oxidation state of the element and its ability to accept or donate electrons. Let's analyze each of the oxides mentioned to determine if they are amphoteric.

1. Mn2O7:
Manganese(VII) oxide (Mn2O7) is a highly acidic oxide and does not show amphoteric behavior. It reacts with water to form the strong acid, permanganic acid (H2MnO4). Therefore, Mn2O7 is not an amphoteric oxide.

2. CrO3:
Chromium(VI) oxide (CrO3) is a strong acid and does not exhibit amphoteric behavior. It reacts with water to form chromic acid (H2CrO4). Hence, CrO3 is not an amphoteric oxide.

3. Cr2O3:
Chromium(III) oxide (Cr2O3) is an amphoteric oxide. It can react with both acids and bases. With acids, it forms salts and water. With bases, it can act as a proton acceptor. The reaction of Cr2O3 with hydrochloric acid (HCl) forms chromium(III) chloride (CrCl3) and water. When it reacts with sodium hydroxide (NaOH), it forms sodium chromite (NaCrO2) and water.

4. CrO:
Chromium(II) oxide (CrO) is a basic oxide. It reacts with acids to form salts and water. However, it does not react with bases. Therefore, CrO is not an amphoteric oxide.

5. V2O5:
Vanadium(V) oxide (V2O5) is an amphoteric oxide. It can react with both acids and bases. With acids, it forms salts and water. With bases, it acts as a proton acceptor. The reaction of V2O5 with hydrochloric acid (HCl) forms vanadium(V) chloride (VCl5) and water. When it reacts with sodium hydroxide (NaOH), it forms sodium vanadate (NaVO3) and water.

6. V2O4:
Vanadium(IV) oxide (V2O4) is a basic oxide. It reacts with acids to form salts and water. However, it does not react with bases. Therefore, V2O4 is not an amphoteric oxide.

In summary, the amphoteric oxides among the ones listed are Cr2O3 and V2O5. They can react with both acids and bases to form salts and water.