It is a popping resonating sound generated by a lean condition on deceleration. When you suddenly close the throttle, the incoming air is choked off and the closed throttle also causes the bike to return to idle on the very lean idle circuit.
The reactivity series of metals was deduced by performing several experiments in the lab which enabled scientists to arrange metals according to their reactivity with dilute acid, oxygen (air), and water.xides of iron and copper are insoluble. Metals that are less reactive than copper like silver, gold and platinum do not react with oxygen. Note: When aluminum reacts with oxygen, a layer of aluminum oxide adheres and covers the aluminum.
An example can be from group 11B-elements like copper, silver, and gold-are commonly cation-making elements with a +1 charge. Copper is different though, because copper often loses 2 electrons for form a +2 charge. You can predict the charges on most nonmetal monatomic ions by the group number and the octet rule.