In IUPAC nomenclature, the correct order of decreasing priority of functional group is :

In IUPAC nomenclature every functional group is assigned a “seniority” (also called order of precedence).
When more than one functional group is present in the same molecule, the group with the higher seniority is chosen for the principal suffix, is given the lowest possible locant, and appears first in the priority list.

A greatly abbreviated portion of the official IUPAC priority table, sufficient for the groups that appear in this question, is:

$$\text{carboxylic acid derivatives (-COOR, -CONH}_{2}\text{ etc.)} \; \gt \; \text{nitrile (-CN)} \; \gt \; \text{aldehyde (-CHO)} \; \gt \; \text{ketone (>C=O)} \; \gt \; \text{alcohol (-OH)} \; \gt \; \text{amine (-NH}_{2}) \; \gt \; \text{alkene (C=C)} \; \gt \; \text{alkyne (C}\equiv\text{C)}$$

For the exact groups that appear in the four options we therefore have, in strictly decreasing priority:

$$-\text{CONH}_{2} \; (\text{carboxamide}) \; \gt \; -\text{CHO} \; (\text{aldehyde}) \; \gt \; >\!\text{C=O} \; (\text{ketone}) \; \gt \; -\text{NH}_{2} \; (\text{amine}) \; \gt \; -\text{C}\equiv\text{C}- \; (\text{alkyne})$$

Now compare each option with this correct sequence:

Option A: $$-\text{CONH}_{2}, >\text{C=O}, -\text{CHO}, -\text{NH}_{2}, -\text{C}\equiv\text{C}-$$ Here the ketone (>C=O) is placed above the aldehyde (-CHO), which violates the table. Hence Option A is wrong.

Option B: $$-\text{CONH}_{2}, -\text{COOCH}_{3}, -\text{CHO}, -\text{NH}_{2}, -\text{OH}$$ Within the acid derivatives an ester (-COOCH₃) outranks an amide (-CONH₂), and alcohol (-OH) outranks amine (-NH₂). Both orders are reversed here, so Option B is wrong.

Option C: $$-\text{CONH}_{2}, -\text{CHO}, >\text{C=O}, -\text{NH}_{2}, -\text{C}\equiv\text{C}-$$ This matches the correct decreasing priority exactly. So Option C is correct.

Option D: $$-\text{CONH}_{2}, -\text{CHO}, -\text{CN}, -\text{NH}_{2}, -\text{C}\equiv\text{C}-$$ The nitrile (-CN) should come immediately after the amide and before the aldehyde, not after it. Therefore Option D is wrong.

Hence the correct order and the correct choice is:
Option C which is: $$-\text{CONH}_2, -\text{CHO}, >\text{C=O}, -\text{NH}_2, -\text{C} \equiv \text{C}-$$