How do you think chemical change is defined?

A chemical change happens when one chemical substance is transformed into one or more different substances, such as when iron becomes rust. Chemical changes occur through the process of chemical reactions, and the resulting substances have different properties because their atoms and molecules are arranged differently.

A chemical change happens when one chemical substance is transformed into one or more different substances,

Explanation:

A.
Cr⁺¹ + Sn⁺⁴ ⇒ Cr⁺³ +Sn⁺²
Cr⁺¹ ⇒ Cr⁺³ + 2e⁻
The half-reaction of oxidation: chrome is an electron donor, losses 2 electrons ie it is oxidized
2e⁻ + Sn⁺⁴ ⇒ Sn⁺²
The half-reaction of reduction: tin is an electron acceptor, receives 2 electrons, ie it is reduced

b.
3Hg⁺² +2Fe ⇒ 3Hg+2Fe⁺³
2Fe ⇒  2Fe⁺³ + 6e⁻ 
The half-reaction of oxidation: iron is an electron donor, losses 3 electrons ie it is oxidized
6e⁻ + 3Hg⁺² + ⇒ 3Hg 
The half-reaction of reduction: mercury is an electron acceptor, receives 2 electrons, ie it is reduced

c.
2As+3Cl₂ ⇒ 2AsCl₃
2As ⇒ 2As⁺³ + 6e⁻ 
The half-reaction of oxidation: arsenic is an electron donor, losses 3 electrons ie it is oxidized
6e⁻ + 3Cl₂ ⇒ 6Cl⁻
The half-reaction of reduction: chlorine is an electron acceptor, receives 1 electron, ie it is reduced

d.
NaBr+Cl₂ ⇒ NaCl+Br₂ 
2Br⁻ ⇒  Br₂ + 2e⁻ 
The half-reaction of oxidation: bromine is an electron donor, losses 1 electron ie it is oxidized
2e⁻ + Cl₂ ⇒ 2Cl⁻
The half-reaction of reduction: chlorine is an electron acceptor, receives 1 electron, ie it is reduced

e.
Fe₂O₃ +3CO ⇒ 2Fe+3CO₂
3C⁺² ⇒ 3C⁺⁴ + 6e⁻
The half-reaction of oxidation: carbon is an electron donor, losses 2 electrons ie it is oxidized
6e⁻ +  2Fe⁺³ ⇒ 2Fe 
The half-reaction of reduction: iron is an electron acceptor, receives 3 electrons, ie it is reduced