Step 1: Define denaturation of proteins.
Denaturation is the disruption of the native three-dimensional structure of a protein by heat, pH changes, heavy metal ions, or organic solvents. The protein loses its biological activity as a result.
Step 2: Review the levels of protein structure.
Primary ($1^\circ$): sequence of amino acids joined by peptide (covalent) bonds. Secondary ($2^\circ$): alpha-helices and beta-sheets stabilized by hydrogen bonds. Tertiary ($3^\circ$): overall 3D shape maintained by hydrogen bonds, disulfide bonds, ionic and hydrophobic interactions.
Step 3: What happens to secondary structure during denaturation?
Hydrogen bonds stabilizing alpha-helices and beta-sheets are broken. So the $2^\circ$ structure is destroyed. Statement 1 (option 1) is TRUE about denaturation.
Step 4: What happens to tertiary structure during denaturation?
All weak interactions (H-bonds, hydrophobic interactions, ionic bonds, van der Waals forces) maintaining the 3D shape are disrupted. So the $3^\circ$ structure is also destroyed. Statement 2 (option 2) is TRUE.
Step 5: What happens to primary structure during denaturation?
The primary structure is the amino acid sequence connected by peptide bonds, which are strong covalent bonds. Denaturation breaks only non-covalent interactions. Peptide bonds are NOT broken during ordinary denaturation. So the $1^\circ$ structure remains intact.
Step 6: Identify the statement that is NOT true.
Option (3) claims that $1^\circ$ structure gets destroyed during denaturation. This is NOT true, because peptide bonds (covalent) are not broken by typical denaturing conditions.
Step 7: State the final answer.
\[ \boxed{1^\circ\ \text{structure gets destroyed -- this is NOT true about denaturation.}} \]