{c}

A <null set> has <Lebesgue outer measure> zero. Equivalently, for every $\varepsilon>0$ it can be covered by countably many open <intervals> whose total length is less than $\varepsilon$. Such a set is automatically <Lebesgue measurable> and has <Lebesgue measure> zero.

Solution

Past exam of the probability, statistics and options I course of the University of Oxford / 2011 / D / 1 / b / Solution

 Solution (source code)