Option 1 -> Total expenditure greater than or equal to income - not affordable.
Option 2 -> Total expenditure strictly less than income - excludes the budget line itself.
Option 3 -> Total expenditure greater than income - clearly unaffordable.
Option 4 -> Total expenditure less than or equal to income - includes all affordable combinations.
Hence, Option 4: P1X1+P2X2≤M -> A budget set represents all combinations of goods that a consumer can afford given their income M and prices P₁ and P₂. The inequality ≤ ensures that total expenditure does not exceed income, including both bundles on the budget line (spending exactly M) and below it (spending less than M). This comprehensively defines all affordable consumption bundles -> correct