Step 1 - Understanding what is a biotic factor
Biotic, as well as other words with "bio" in them, is related to living organisms. A biotic factot is, therefore, a factor which depends on living organisms. When living organisms shape their environment, as well as other living beings environments, we call it a "biotic factor".
Step 2 - Using the definition to solve the exercise
a) Competition among predators: since this is a consequence of the struggling between two or more living beings, the outcome of it is surely a biotic factor. Individuals can die because they could not find enough food due to competition. A population could thus be modified by this biotic factor, for example.
b) A disease caused by bacteria: a bacteria is a living being and a disease can disastrously kill an entire population, radically changing the ecological relations and the environment. This is another biotic factor.
c) Invasive species: this is also caused by living beings. When a specie invades another species territory, there may be fight among them or just resources sharing. Either way, the ecological relations will be drastically modified. This accounts for a biotic effect as well.
d) weather: this is not solely caused by living beings. In fact, it depends rather poorly on living beings, and much more on Earth's temperature, geographical location an so on. Since the changes caused by weather are not from a living source, this is not a biotic factor.
The answer is thus item d.
