Which of the following substances has a standard heat of formation δh°f of zero? choose one or more: a. pb at 1000°c b. c3h8 (g) at 25.0°c and 1 atm pressure c. solid glucose at room temperature d. n2(g) at 25.0°c and 1 atm pressure

Answer : The correct answer is option D.  N₂(g) at 25.0°C and 1 atm pressure

Explanation :

Standard heat of formation defined as the change in heat when one mole of a compound is formed from its elements in standard state.

Therefore all the substances which are compounds will have some value of heat of formation.

On the other hand, a substance will have zero heat of formation when it is present in elemental form and in its standard state at STP

If we take a look at the given options, we can see that Pb and N₂ exist in elemental forms.

But we have Pb at 1000° C. Melting point of Pb is around 620° C. Above this temperature, Pb will be present in liquid state which is not its standard state.    (standard state of Pb is solid as it is a metal)

Therefore the only substance that is present in elemental form and in its standard state is N₂.

The correct option is N₂ (g) at 25°C and 1 atm

a rain shadow is a dry region of land on the side that is protected against the prevailing winds of a mountain range. the prevailing winds are the winds that occur most of the time in a particular place of the earth

prevailing winds carry air toward the mountain range. as the air rises up over a mountain range, the air cools, water vapor condenses, and clouds form. on this side of the mountains, called the windward side, precipitation falls in the form of  rain  or snow. this dry air produces a  rain shadow.

a) the particles of the chair are strongly held together.