Coenzymes
Coenzymes are small organic molecules that, themselves, do not function as catalysts (i.e. enzymes) but aid the latter in carrying out their functions. Enzymes are biological catalysts, which means that they allow reactions to occur at lower activation energies. In a way, enzymes help to "speed up" chemical reactions.
Coenzymes are mostly derived from vitamins. Examples include TPP from Vitamin B1 (thiamine), FAD from Vitamin B2 (Riboflavin), and NAD+ from Niacin.

<h2>Fixation</h2>
Nitrogen in its gaseous form (N2) can’t be used by most living things. It has to be converted or ‘fixed’ to a more usable form through a process called fixation. There are three ways nitrogen can be fixed to be useful for living things:
<h3>Biologically: </h3>
Nitrogen gas (N2) diffuses into the soil from the atmosphere, and species of bacteria convert this nitrogen to ammonium ions (NH4+), which can be used by plants. Legumes (such as clover and lupins) are often grown by farmers because they have nodules on their roots that contain nitrogen-fixing bacteria.
<h3>Through lightning: </h3>
Lightning converts atmospheric nitrogen into ammonia and nitrate (NO3) that enter soil with rainfall.

In a typical ECG (Electrocardiogram) the first wave obtained is P wave; The P wave represents the depolarization of the atria. After this, the QRS complex is formed. The QRS wave represents the depolarization of the ventricles. During the depolarization phase, the ventricles contracts and pushes the blood into the atria. Hence, the correct answer is depolarization of the ventricles.