Which one of the following is a double-displacement reaction?
~there can be more then one answer~

a. 2h2 (g) + o2 (g) → 2h2o (g)
b. 2h2o (l) → 2h2 (g) + o2 (g)
c. naoh (aq) + hcl (aq) → nacl (aq) + hoh (l)
d. cu (s) + 2agno3 (aq) → cu(no3)2 (aq) + 2ag (s)

In which of the following cases is work being done on an object? question 2 options: pulling a trailer up a hill carrying a box down a corridor suspending a heavy weight with a strong chain pushing against a locked door

You throw a small rock straight up from the edge of a highway bridge that crosses a river. the rock passes you on its way down, 7.00 s after it was thrown. what is the speed of the rock just before it reaches the water 28.0 m below the point where the rock left your hand? ignore air resistance.

Two conductors, a and b, are each in the shape of a tetrahedron. but of different sizes. they are charged in the following manner: 1. tetrahedron a is charged from an electrostatic generator to charge q. 2. tetrahedron a is briefly touched to tetrahedron b. 3. steps 1 and 2 are repeated until the charge on tetrahedron b reaches a maximum value. if the charge on tetrahedron b was q/4 after the first time it touched tetrahedron a. what is the final charge qbmax on tetrahedron b?