pPlease correct my writing.

lLife or living.

In this context: scientifical developments have improved the quality of life/living, and in this context: scientifical developments have improved many aspects of life/living ¶
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Starting at nearly x in w, males who were tThailand’s streongesth members experienced a dramatic increase to approximately (number?) before gradually decreasing to (number?) and then rising again to a peak of y in z.

Both are fine. Almost the same meaning. Living specifically means right now, in this moment. Quality of life usually means right now too, but can also refer to any time.

Finally, the figures for males and females dropped again, reacheding x for males and y for females.

I want to ask if iI can use reach with the trend :decrease”s or if I can only use it with the trend increases?

Reach can be used with decrease, but "fell to" is better. Reach generally means something is going up.

iIndia had far more elephants than (the) other countries in both years despite having the largest decrease.

The number of elephants in India was the largest, at 10,000, but then had decreased significantly byto approximately 3000 by 2004.

By is fine, but since you are using it twice in one sentence, switch the first one to "to".

Meanwhile, tThailand had nearly 4000 elephants in 1997 and also experienced a loss, but smaller, of about 2,000.

In 1950, there was a housing area to the west of the school and a main road to the north which runs from west to east .

We usually say "east to west" but if west to east is correct it's fine.

Overall, the most notable changes in 2000 were that the school property had doubled in size with more facilities, including a sports field and a science block, a. As for 2010, they were the expansion of parking spotding (the number of parking spots / the parking lots) and relocation ofng the sports field.

Overall, West Park Secondary School only ocontained one building and a playground in 1950 and was located near residential and agricultural land.

By 2010, the school’s property had been expanded for the introduction of several facilities, coincluding a science block and a cr park and there was the notable addition of a large car park.

"Concluding" means "to finish something"

In 1950, there was a main road running weast-weast to the north of the school, while to the west was a housing area.

Again, east-west is more common.

tThere was a housing area to the west of the school and a main road to the north which runsan from weast to weast .

Both already sound natural. No need to change them.

To show my grammar knowledge, I want to add the past perfect tense to my essays.

Is my use of it correct in this sentence: bBy 2020/after 30 years, the playground had remained unchanged, while the farmland had been changed into a sports field.

Looks great!

After 30 years, the main road, the science block, and the school were still there (1).

Can “remain intact” and “remained original” be used in this context, or ido I have to use “remiained unchanged/the same”?

"Remain intact" = it was not broken
"Remained original" = it was not replaced by another building or thing
"Remain unchanged/the same" = there was not any change at all

They are similar, but a little different. You can sometimes use them instead, but you have to make sure it matches your facts.

In addition, a new small sports field was built ion the west side of the playground and took up approximately one-third of its area.