To determine the order of decreasing bond length for the given molecules or ions, we need to consider the nature of the atoms involved and their bond types. Here's the order:
1. (c) The CN bond in HCN (triple bond)
2. (a) The CO bond in CO (triple bond)
3. (b) The SO bond in SO2 (double bond)
Now, let's explain the reasoning
(a) The CO bond in CO: This is a triple bond between carbon and oxygen. Triple bonds are shorter and stronger than double bonds or single bonds. Therefore, the CO bond in CO is shorter than both of the other bonds.
(b) The SO bond in SO2: This is a double bond between sulfur and oxygen. Double bonds are longer than triple bonds but shorter than single bonds. So, it is longer than the CO triple bond but shorter than the CN triple bond.
(c) The CN bond in HCN This is a triple bond between carbon and nitrogen. As mentioned earlier, triple bonds are the shortest and strongest. Therefore, the CN bond in HCN is the longest among these options.
So, the order of decreasing bond length is (c) > (a) > (b).