A ....... experiment is a process whose outcome is undetermined.
A. Variable
B. Random
C. Event
D. Sample

Hint: Let us suppose, if we toss a coin then either head or tail will come but, we are not able to predict the exact outcome of the experiment that a head or tail will come. Hence, the outcome of this experiment is undetermined and such type of experiment is known as random experiment.

Complete step-by-step answer:
We have been asked to find the experiment in which the outcome is undetermined.
Let us take an example of rolling a die having six faces numbered as 1, 2, 3 .... 6. But before rolling a die we do not know the result. This is an example of a random experiment whose outcome is undetermined. We can only find the all possible outcomes known as sample space of the experiment. For the above experiment, sample space is,
\[S=\left\{ 1,2,3,4,5,6 \right\}\]
Therefore, the correct option is B.

Note: Remember that, a random experiment is a process by which we observe something uncertain and an outcome is a result of a random experiment and a set of all possible outcomes is known as sample space denoted as S. Example of random experiment is tossing a coin.