A sultan is the leader of a sultanate (e.g., Oman). The Mughal leaders are usually called emperors, which is the western equivalent of their actual title, Padishah / Shahanshah (king of kings).
The first Mughal emperor Babur conquered the Sultanate of Delhi, so "Sultan of Delhi" was probably among his many lesser titles.
The leader of the first successful expedition to the summit of Mt Everest was Sir John Hunt. From his expeditionary party, Hunt selected two pairs of climbers to attempt the final ascent, and Hillary and Tenzing Norgay were the second pair chosen. They only set out after the first pair, Tom Bourdillon and Charles Evans, were forced to turn back by the weather. Hunt himself reached 8350 metres, 500 metres below the summit, to leave an equipment cache for Hillary and Norgay.
It might make for a long list of stats, but I still think it would be good to see the percentages of people guessing each question correctly. Obviously that would mean tracking which random set of questions was thrown up each time, but I suspect it can be done!
Pripyat should be an accepted type in for the nuclear disaster question - I believe geographically it's more correct for "Where" the disaster happened than Chernobyl (although the plant was named after the more distant city)
In the question "whose improvements to the steam engine helped trigger the industrial revolution" while Watt is a good and correct answer Trevithick should also be an aswer. Watt invented the negative pressure steam engine which allowed pumps/factory machinery etc while trevithick invented the high pressure steam engine which allowed locomotives/agricultural engines etc
"What was the largest German state when Germany was united?" is somewhat ambiguous---this can refer to either German unification in 1871 or 1990. Probably best to add the year.
This question should be revised to ask, "What was the first empire to unite most of India?" The southern tip of the mainland and Sri Lanka were not part of Mauraya. Indeed, I am not sure the Indian subcontinent has ever been an entirely unified state, even under the British.
The first Mughal emperor Babur conquered the Sultanate of Delhi, so "Sultan of Delhi" was probably among his many lesser titles.