"The girl is happy with her red dress."
Translation:La niña está feliz con su vestido rojo.
i used ser instead of estar and was marked correct. But when I thought about it a bit more, it seemed to me that ser doesn't seem correct in this case, since the girl is in the state of happiness and hence only estar should be correct. So am I thinking correct or there is something that I am missing?
Feliz is one of the few adjectives that you can use either with ser or with estar with little meaning change. Notice that with contenta you can only use estar and with alegre you could use both, but only estar in this particular sentence.
La niña es/está feliz con su vestido rojo.
La niña está contenta con su vestido rojo.
La niña está alegre con su vestido rojo.
According to this link, it is a difference in how happy someone is. Felíz is "over the moon" happy while contento/a is a "meh.. I am content/satisfied" sort of happy.
If she just bought the dress and it is for a special occasion, say a prom, then she would be felíz, very happy, where as if it just a dress like any other dress, she may just be "content" with the dress.
I agree, but how are we to know from the context of the sentence which is correct. Seems to me both should be acccepted.
"rojo vestido" es incorrecto? ...es singular y masculino. porqué no se puede poner el adjetivo antes de el sustantivo?
Usually. Grande can go before a noun. When it does, it becomes gran, and become more emphasized.
why is there a su here? su is a replacement for tu when you are talking to someone older or someone you respect, right? or is there something i am missing
"su" can also mean "her" or "his."
This is probably more information that you want, but it is a handy all around guide: