Exam boards have been told to raise their game after another rogue question appeared on an AS-level exam paper – the third this summer.
Students were left baffled by a multiple-choice question in a biology paper they took in May. The exam board concerned has admitted that all the answers students could choose were wrong.
Edexcel, which set the paper, said the question was worth one mark out of a possible 425 and promised markers would adjust scores to ensure no candidate was disadvantaged.
A business studies paper set by the AQA exam board left out crucial information so pupils were unable to answer one question, it emerged last month. The question, worth three marks, asked students about the profits a fictional chocolate a company was making, but examiners failed to include all the information about the company.
Days earlier, the OCR board included an "impossible" question in a maths AS exam. Students were asked to solve an equation without the information needed to do so.
Edexcel, AQA and OCR are the biggest exam boards in the country.
Students fear the time wasted on rogue questions may mean they fail to achieve the grades they need for places at their preferred universities.
One student who took the business studies paper told a tutoring website the exam started "with a bang. Then came the killer blow – I wasted quite a bit of time looking for the information." He had answered the rest of the paper "in an agitated, nervous manner".
One student who took the biology paper told the BBC: "This was a retake for me, so the time I lost spent on that question could possibly have cost me a university place, right before the fees go up."
Ofqual said it expected exam boards to meet the highest standards when preparing exam papers.