Let C_{V} and C_{P} denote the molar heat capacities of an ideal gas at constant volume and constant pressure respectively. Which of the following is a universal constant?

For an ideal gas, C_{p} - C_{v} = R.

Here, R is the universal gas constant.

Hence, the correct option is (c).

Option (a) is incorrect since C_{p}/C_{v} = ℽ, which differs for monoatomic, diatomic or polyatomic gases. Here ℽ = ratio of molar heat capacities at constant pressure and constant volume.

Option (b) is incorrect since C_{p}C_{v} = ℽC_{v}^{2}, which is not a constant as ℽ varies.

Option (d) is incorrect since C_{p} + C_{v} = (ℽ+1)C_{v}, which is not a constant as ℽ varies.

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