Answer:
Combination or synthesis
Explanation:
The reaction is a combination or synthesis reaction in which two or more substances combines to give a single product.
In such a reaction there is formation of compounds from the union of their constituent elements.
The driving force for such reactions is the large and negative heat of formation of the product.
So, this is a combination reaction.
True, They contain old stars and posses little gas or dust
Here we have perfectly inelastic collision. Perfectly inelastic collision is type of collision during which two objects collide, stay connected and momentum is conserved. Formula used for conservation of momentum is:

In case of perfectly inelastic collision v'1 and v'2 are same.
We are given information:
m₁=0.5kg
m₂=0.8kg
v₁=3m/s
v₂=2m/s
v'₁=v'₂=x
0.5*3 + 0.8*2 = 0.5*x + 0.8*x
1.5 + 1.6 = 1.3x
3.1 = 1.3x
x = 2.4 m/s
This would be typical of an elastic collision.