A gas expands isothermally against a constant external pressure of 1 bar from 10 dm$^3$ to 20 dm$^3$ by absorbing 800 J of heat from surrounding. Calculate value of $\Delta$U.

Which from following decides the rate of multistep reaction?

What is minimum number of spheres required of develop a tetrahedral void?

Which from following ionic solids exhibits decrease in its solubility in water with increase of temperature?