For which of the following liquid mixtures $\Delta_{\text{mix}}H=0$ and $\Delta_{\text{mix}}V=0$?

An ideal solution is that which

What is vapour pressure? And what is an ideal solution?

Liquids $A$ and $B$ form an ideal solution for all compositions of $A$ and $B$ at $25^{\circ} C$. Two such solutions with $0.25$ and $0.50$ mole fractions of $A$ have total vapor pressures of $0.3 \ bar$ and $0.4 \ bar$,respectively. What is the vapor pressure of pure liquid $B$ in $bar$?

Two liquids $X$ and $Y$ form an ideal solution. At $300 \ K,$ vapour pressure of the solution containing $1 \ mol$ of $X$ and $3 \ mol$ of $Y$ is $550 \ mm \ Hg.$ At the same temperature,if $1 \ mol$ of $Y$ is further added to this solution,vapour pressure of the solution increases by $10 \ mm \ Hg.$ Vapour pressure (in $mm \ Hg$) of $X$ and $Y$ in their pure states will be,respectively:

Mixing $1 \ mol$ of heptane $(V.P = 92 \ mm \ Hg)$ with $4 \ mol$ of octane $(V.P = 31 \ mm \ Hg)$ forms an ideal solution. The vapor pressure of the solution will be .......... $mm \ Hg$. (in $.2$)