A solution contains some or all of the ions Cu2 , Al3 , K , Ca2 , Ba2 , Pb2 , and NH4. The following tests were performed, in order, on the solution. Addition of 6 M HCl produced no reaction. Addition of H2S with 0.2 M HCl produced a black solid. Addition of (NH4)2S produced a white solid. Addition of (NH4)2HPO4 in NH3 produced no reaction. The final supernatant when heated produced a purple flame. Identify which of these ions were present in the solution, which were absent, and for which ones no conclusions can be drawn.
bins are: present. absent. and Inclusive.
options: K+ Ba2+ NH4+ Al3+ Pb2+ Ca2+ Cu2+

c-14 is carbon-14, or radiocarbon.   it is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.

it is stable as it is in group 0 which have full outer shells of electrons

a). in this case, dh> 0 and sd> 0. if t becomes larger, the term "-tds" will become more negative. at some point, it is possible that -dts will be more negative than the dh is positive, and the reaction will become spontaneous. this is probably the correct answer, but you should look at all of the other possibilities and make sure of that.

answer: semi-infinite solid initially at a uniform temperature of 400 ◦c is cooled at its surface by convection. the cooling fluid at a constant temperature of 200 ◦c has a convective coefficient (ha) of 250 w/m2.k. the physical properties of the solid: k = 20 w/m.k and α = 4 * 10-5  m2/s. using δx = 0.04 m and δt = 10 s. write the finite difference equations describing the transient heat transfer of the first five δx and the temperature profile after 30 s.