Answer - When the application is running in development mode, React will automatically check all props that we set on components to make sure they have correct type. If the type is incorrect, React will generate warning messages in the console. It's disabled in production mode due to performance impact. The mandatory props are defined with isRequired. The set of predefined prop types: i. PropTypes.number ii. PropTypes.string iii. PropTypes.array iv. PropTypes.object v. PropTypes.func vi. PropTypes.node vii. PropTypes.element viii. PropTypes.bool ix. PropTypes.symbol x. PropTypes.any We can define propTypes for User component as below: import React from 'react' import PropTypes from 'prop-types'