Which statements describe how stars are born? Check all that apply. Stars are born in clouds of gas and dust called nebulas. The gas and dust are pulled together by gravity. If the cloud that is pulled together has enough mass, a red giant is formed. The pulled-together cloud collapses and becomes hot and dense. Heat and pressure cause nuclear fusion, which signals the birth of a star.

1.Stars are born in clouds of gas and dust called nebulas.

2.The gas and dust are pulled together by gravity.

4.The pulled-together cloud collapses and becomes hot and dense.

5.Heat and pressure cause nuclear fusion, which signals the birth of a star.

Explanation:

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2