**Core Concept**
Immunoglobulins, also known as antibodies, are crucial components of the adaptive immune system, responsible for recognizing and neutralizing pathogens. Their structure is composed of multiple polypeptide chains, which provide specificity and functionality. Understanding the composition of immunoglobulins is essential for appreciating their role in immunity.

**Why the Correct Answer is Right**
The correct answer, C, highlights an important aspect of immunoglobulin structure. Each antibody molecule consists of two identical heavy (H) chains and two identical light (L) chains, which are linked by disulfide bonds. These chains are arranged in a specific configuration, with the H chains forming the backbone and the L chains protruding from the H chains. This arrangement allows for the recognition of antigens and the activation of immune responses.

**Why Each Wrong Option is Incorrect**
**Option A:** The statement that immunoglobulins are a Y-shaped heterodimer composed of four polypeptide chains is partially correct, but it omits the crucial detail that two of these chains are identical. The Y-shape is indeed characteristic of immunoglobulin structure, but the heterodimeric nature is more nuanced.
**Option B:** The claim that all four H and L chains are bound to each other by disulfide bonds is incorrect. While the H and L chains are indeed linked by disulfide bonds, the two H chains and the two L chains are also linked to each other, forming a more complex network of disulfide bonds.
**Option D:** The statement that there are 5 classes of H chains and two classes of light chains is incorrect. There are five classes of immunoglobulins (IgA, IgD, IgE, IgG, and IgM), but each of these classes can have multiple types of heavy and light chains.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the structure of immunoglobulins is closely related to their function, and the arrangement of H and L chains determines the specificity and affinity of the antibody for its antigen. This understanding is critical for the development of vaccines and immunotherapies.

**✓ Correct Answer: C. Antibody contains two types of light chain and one type of heavy chain**