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

If $^nP_4 = 30 \times ^nC_5$,then $n = \dots$

When electric current is passed through acidified water for $1930 \ s$,$1120 \ mL$ of $H_2$ gas is collected (at $STP$) at the cathode. What is the current passed in amperes?

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

$A$ proton of mass $1.67 \times 10^{-27} \, kg$ and charge $1.6 \times 10^{-19} \, C$ is projected with a speed of $2 \times 10^6 \, m/s$ at an angle of $60^{\circ}$ to the $X$-axis. If a uniform magnetic field of $0.104 \, T$ is applied along the $Y$-axis,the path of the proton is:

What is the role of limestone during the extraction of iron from haematite ore?