Option 1 -> The slope of the budget line is (-)P₁/P₂, representing the negative price ratio of the two goods.
Option 2 -> P₁/P₂ lacks the negative sign, which is essential to show the inverse relationship between the two goods.
Option 3 -> (-)P₂/P₁ is the inverted price ratio and does not correctly represent the budget line slope.
Option 4 -> P₂/P₁ is inverted and also missing the negative sign.
Hence, Option 1: (-)P₁/P₂ -> The budget line equation is P₁X₁ + P₂X₂ = M. Rearranging: X₂ = M/P₂ - (P₁/P₂)X₁. The slope (coefficient of X₁) is -(P₁/P₂). The negative sign indicates the trade-off: to consume one more unit of Good 1, you must sacrifice (P₁/P₂) units of Good 2. This reflects the opportunity cost and the downward-sloping nature of the budget line. -> correct