Hydrogen bonding is an attractive force that plays a key role in determining the physical properties of molecular substances. what features are required for a substance to experience hydrogen bonding among its own molecules?

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).

there is none because earth is stationary and flat.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.