Option 1: c -> This represents the marginal propensity to consume (MPC), which is the slope of the consumption function.
Option 2: Cˉ -> This is autonomous consumption, representing the intercept (consumption when income is zero), not the slope.
Option 3: cY -> This represents induced consumption (the income-dependent part of consumption), not the slope.
Option 4: Y -> This is income, the independent variable in the consumption function, not the slope.
Hence, Option 1: c -> In the consumption function C = Cˉ + cY, the parameter 'c' is the marginal propensity to consume (MPC), which represents the slope. It shows the change in consumption for each unit change in income (ΔC/ΔY). The value of c lies between 0 and 1, indicating that for every additional dollar of income, consumption increases by c dollars. -> correct