What is the correct order of occurrence ($\%$ by weight) in air of $Ne, Ar$ and $Kr$?

Two blocks $A$ and $B$ of masses $1\,kg$ and $2\,kg$ are connected together by a spring and are resting on a horizontal surface. The blocks are pulled apart so as to stretch the spring and then released. The ratio of $K.E.s$ of both the blocks is

Which of the following components of cement is present in the highest amount?

Let $A$ and $B$ be subsets of a set $X$. Then

Three blocks,$A, B$ and $C,$ of masses $4\,kg, 2\,kg$ and $1\,kg$ respectively,are in contact on a frictionless surface,as shown. If a force of $14\,N$ is applied on the $4\,kg$ block,then the contact force between $A$ and $B$ is ....... $N$.

The locus of the centre of a circle which passes through the origin and cuts off a chord of length $4$ units from the line $x=3$ is