Question

An experiment to determine the effect of cigarette smoking on lung cancer

Whats the hypothesis?

Answer 1

That's an interesting question to ask and an informative question.
Hypothesis is what one's think that is going to happen in the the experiments and what will be the result . so, according to this the hypothesis here will be like that " cigarette smoking is the  cause  of lung cancer"
Or "cigarette smoking is one of the cause of lung cancer"
It depends on you who you see it and also you can create your work of hypothesis from this.

Moreover hypothesis is the way to theory in scientific method which ultimately help in making law of the world by proving again and again through experiment 

Answer 2

Hypothesis in scientific research is defined as a proposed statement or allegation that is given as a starting  explanation for further investigation of a certain topic.

Hypothesis usually take the form of :

"If........then"

Here are examples of hypothesis that can be used for this experiment:

1) Cigarette smoking causes lung cancer  

2) If you smoke less than a packet of cigarette per week then you will not develop lung cancer.

3) If you smoke more that 3 packets of cigarette per week then you are likely to develop lung cancer.