If a person has bp 155/100 for one month can all this happen in one month chemical reactions due to which ldl cholesterol being oxidized and plaque formation if person bp is normal after one month is he still at risk of developing atherosclerosis?

Atherosclerosis takes years to develop and the scenario you describe- no

The high blood pressure almost always related to eating more salt than your kidneys can dump without increasing your BP. High BP accelerates atherosclerosis. The major risks at your age are stroke and kidney failure. Over time the atherosclerosis you likely have now in your aorta (fatty streaks) will clog up & cause heart disease/aneurysm of aorta/block arteries to penis. Get BP down and BMI 25