Which of the following is $NOT$ produced by the reaction of ethanol with $H_2SO_4$?

The curve between charge density and distance near a $P-N$ junction will be:

Animals devoid of respiratory,excretory,and circulatory organs are:

If a number is chosen at random from the four-digit numbers formed by using the digits $0, 1, 2, 3, 4, 6$ without repetition,then the probability that it is divisible by $4$ is:

Four cards are drawn at random from a pack of playing cards. The probability of getting exactly two cards from the same suit and the remaining two cards from two different suits is

The half-life of $Ra^{226}$ is $1620$ years. Calculate the number of atoms that decay in one second in $1 \ g$ of radium (Avogadro number $= 6.023 \times 10^{23}$).