Alpha-helix is found in which level of protein structure ?

(A) Secondary structure
The primary structure of a protein refers to the linear sequence of amino acids.
The secondary structure refers to the local folded structures that form within a polypeptide due to interactions between atoms of the backbone. The most common types of secondary structures are the \(\alpha\)-helix and the \(\beta\)- pleated sheet.
The tertiary structure is the overall three-dimensional structure of a polypeptide.
The quaternary structure is the arrangement of multiple folded protein or coiling protein molecules in a multi-subunit complex.
Therefore, the \(\alpha\)-helix is found in the secondary structure of proteins.