The coefficient of price elasticity of demand measures the responsiveness of quantity demanded to a change in price. It is calculated by dividing the percentage change in quantity demanded by the percentage change in price.

In this case, the price of the commodity increases from Rs. 90 to Rs. 110, which is a 22.22% increase [(110 - 90) / 90 * 100]. The quantity demanded reduces from 240 units to 160 units, which is a 33.33% decrease [(240 - 160) / 240 * 100].

Now, we can calculate the price elasticity of demand using the formula:

Price Elasticity of Demand = (Percentage Change in Quantity Demanded) / (Percentage Change in Price)

= (-33.33%) / (22.22%)

= -1.5

The coefficient of price elasticity of demand is negative because there is an inverse relationship between price and quantity demanded. However, since the coefficient is greater than 1, we can say that the demand for this commodity is elastic, meaning that the quantity demanded is highly responsive to changes in price.

Therefore, the correct answer is option 4.