The opposite of an acid is a base, and that's exactly what an antacid is. Antacids make you feel better by increasing the pH balance in your stomach. The pH system is a scale for measuring the acidity or alkalinity of a given environment (in this case, your stomach). The scale goes from 0 to 14. A pH of 7 is neutral. Below 7 is acid. Above 7 is alkaline.
Economy is the large set of inter-related economic production and consumption activities which aid in determining how scarce resources are allocated.
A market economy is an economy where most resources are owned and controlled by individuals and are allocated through voluntary market transactions governed by the interaction of supply and demand. People exchange resources, such as money, for other resources, such as goods or services, on a voluntary basis in the market.