Heating $(NH_4)_2Cr_2O_7$ liberates a gas. The same gas is obtained by:

The circuit diagram shows a logic combination with the states of outputs $X, Y$ and $Z$ given for inputs $P, Q, R$ and $S$ all at state $1$. When inputs $P$ and $R$ change to state $0$ with inputs $Q$ and $S$ still at $1$,the states of outputs $X, Y$ and $Z$ change to:

The species having tetrahedral shape is

Which of the following is not a polyamide?

There is a horizontal film of soap solution. On it,a thread is placed in the form of a loop. The film is pierced inside the loop,and the thread becomes a circular loop of radius $R$. If the surface tension of the soap solution is $T$,then what will be the tension in the thread?

During transcription,the site on $DNA$ where $RNA$ polymerase binds is called .........