When carbon dioxide is passed through limewater, it turns milky due to the formation of calcium carbonate. The reaction involved is given below:

${\text{Ca(OH)}}_2\text{(aq)}+{\text{CO}}_2\text{(g)}\to {\text{CaCO}}_3\text{(s)}+{\text{H}}_2\text{O}\text{(l)}$

Sublimation refers to a change of state from solid to gas without the intermediate formation of a liquid.Usually, the gas returns to the solid state on cooling. Here, solid iodine converts to violet vapours of iodine.

When carbon dioxide is passed through lime water, it turns lime water milky due to formation of calcium carbonate.

When magnesium oxide is dissolved in water, magnesium hydroxide is formed. So, the reaction between magnesium oxide and water is a chemical change, as a new substance(magnesium hydroxide) is formed.

$MgO+H_{2}O\to Mg(OH{)}_2$

A change can be physical or chemical, depending on whether or not it involves the formation of a new substance.
In a physical change, the product formed has the same properties as the original substance whereas, in a chemical change, the product formed has different properties than the original substance. Some of the examples of physical changes are melting of ice, cutting a fruit,etc. Some of the examples of chemical changes are burning of wood, rusting of iron, etc.

Two methods by which rusting of iron can be prevented are Painting and galvanizing.

The statue is made of the same stone and changes made during the making of statue changes the physical properties of a substance. Hence, this kind of change is known as a physical change. It is not a chemical change because no new substance is formed as only the shape (physical property) of the stone is changed.

Changes in which new substances are formed are called chemical changes.
Chemical changes occur when a substance combines with another to form a new substance, called synthesis or, alternatively, decomposes into two or more different substances. At the molecular level, chemical change involves making or breaking of bonds between atoms.

A change in which new substance is formed, whose composition and properties are different from those of the original substance is known as a chemical change. The change is permanent and cannot be reversed. So, chemical changes are mostly irreversible and physical changes are reversible. Hence, the given statement is true.