Three numbers are chosen at random from $1$ to $20$. The probability that they are consecutive is

Two identical $5\,kg$ blocks are moving with the same speed of $2\,m/s$ towards each other along a frictionless horizontal surface. The two blocks collide,stick together,and come to rest. Considering the two blocks as a system,the work done on the system by the external forces will be .............. $Joule$.

The figure given below shows a small part of human lung where exchange of gases takes place. In which one of the options given below,the one part $A, B, C$ or $D$ is correctly identified along with its function?

Reduction in $pH$ of blood will

The plant group that lives in an amphibious state between algae and pteridophytes is known as ......

The pair of straight lines is represented by the equation $3dx^2 - 5xy + (d^2 - 2)y^2 = 0$. If the lines are perpendicular to each other,for how many values of $d$ will this condition be satisfied?