What does the given structural formula represent?

Which logic gate is represented by the following combination of logic gates?

In humans,the sinus venosus is considered to have merged with the wall of which chamber?

Perhydrol is an aqueous solution of

In a book of $500$ pages,it is found that there are $250$ typing errors. Assume that Poisson law holds for the number of errors per page. Then,the probability that a random sample of $2$ pages will contain no error,is :

Two identical capacitors have the same capacitance $C$. One of them is charged to potential $V_1$ and the other to $V_2$. The negative ends of the capacitors are connected together. When the positive ends are also connected,the decrease in energy of the combined system is