The magnitude of price elasticity for an individual good is determined by several factors. Firstly, it is influenced by the degree to which the good is a necessity or luxury. Goods that are considered necessities tend to have inelastic demand, meaning that changes in price have a relatively small impact on the quantity demanded. On the other hand, luxury goods often have elastic demand, meaning that changes in price have a larger impact on the quantity demanded.

Secondly, the extent to which substitutes are available affects the price elasticity. When there are many substitutes available for a particular good, consumers have more options to choose from, making the demand for that good more elastic. In contrast, if there are few or no substitutes, the demand tends to be more inelastic.

Thirdly, the relative importance of the good in the consumer`s budget is also a determining factor. If a good represents a significant portion of an individual`s budget, they are likely to be more sensitive to changes in price, resulting in elastic demand.

Therefore, the correct answer is option 3 (1, 2, and 4), as all three factors mentioned - necessity or luxury, availability of substitutes, and the relative importance of the good in the consumer`s budget - contribute to determining the magnitude of price elasticity.