Cesium Sulfide
No, cesium is an element.
Cesium doesn't have a smell you need special equipment to detect Cesium.
cesium will sink
Yes, Cesium cyanide is soluble as are all cesium compounds.
Cesium Chloride can only conduct electricity in water or while molten. Once cesium chloride is in a solid state it will not conduct electricity.
Cesium Sulfide
As you did not specify an isotope of cesium, I will assume you meant natural cesium. Natural cesium is not radioactive so it does not decay. There will always be the same 10 g of cesium, no matter how long you wait.
No, cesium has no odor.
No, cesium is an element.
With a stop watch or a clock. If you're asking how do we determine what a second is (In the SI- International system of units), then that is determined by the oscillation of a Cesium Atom's Microwave. No matter what the conditions, the cesium atom's full oscillation will always equal one second. No matter where in the world. Really neat phenomenon.
Cesium doesn't have a smell you need special equipment to detect Cesium.
No cesium is a solid metal.
Cesium is extremely reactive.
cesium will sink
Yes, Cesium cyanide is soluble as are all cesium compounds.
The high reactivity of cesium comes from its tendency to give up the one electron in its outermost shell and become a cesium 1+ ion, which is more stable. In cesium chloride, the cesium is already in its stable ionic form.