At high temperatures,which of the following are present?

Doctors use a stethoscope to hear the sounds produced during each cardiac cycle. The second heart sound is heard when:

The molarity of pure water is

Consider the circle $x^2+y^2-4x-2y+c=0$ whose centre is $A(2,1)$. If the point $P(10,7)$ is such that the line segment $PA$ meets the circle at $Q$ with $PQ=5$,then $c$ is equal to

Which fibrous mineral substance can withstand red-hot temperatures without being damaged?

Which of the following reactions will $NOT$ occur with heated copper at $300\,^\circ C$?