During glycolysis, the oxidation of 3-phosphoglyceraldehyde (PGAL, also known as glyceraldehyde-3-phosphate or G3P) is a key step.

The enzyme glyceraldehyde-3-phosphate dehydrogenase catalyzes the oxidation of PGAL. In this reaction, PGAL is oxidized to 1,3-bisphosphoglycerate (BPGA).

During the oxidation of PGAL, hydrogen atoms (and electrons) are removed from PGAL. These are transferred to the coenzyme NAD$^+$, which gets reduced to NADH and a proton (H$^+$). So, NAD$^+$ is reduced to NADH + H$^+$.

In this specific step, an inorganic phosphate ($P_i$) is added to PGAL to form BPGA. This step does not directly consume or produce ATP. However, in the very next step of glycolysis, 1,3-bisphosphoglycerate (BPGA) is converted to 3-phosphoglycerate (PGA), and during this conversion, a phosphate group is transferred from BPGA to ADP to form ATP via substrate-level phosphorylation.

• (A) PGAL is oxidised to BPGA, transferring hydrogen atoms to NAD+, and ATP is consumed in the process.

  • The oxidation and NAD$^+$ reduction are correct. However, ATP is not consumed in this step.

• (B) PGAL is oxidized to BPGA, NAD+ is reduced to NADH + H$^+$, and ATP is directly formed in this step.

  • The oxidation and NAD$^+$ reduction are correct. However, ATP is not directly formed in this specific step.

• (C) PGAL is oxidized to BPGA, NAD+ is reduced to NADH + H$^+$, and ATP is later formed during the conversion of BPGA to 3-phosphoglyceric acid (PGA).

  • This statement accurately describes the oxidation of PGAL to BPGA, the reduction of NAD$^+$ to NADH + H$^+$, and correctly states that ATP is formed in the subsequent step when BPGA is converted to PGA.

• (D) PGAL is directly converted to ATP and CO$_2$, releasing energy without involvement of NAD+.

  • This statement is incorrect. PGAL is not directly converted to ATP and CO$_2$. CO$_2$ is not produced in glycolysis, and NAD$^+$ is definitely involved.

Therefore, option (C) provides the most accurate description.

The final answer is $\boxed{\text{C}}$