Option 1 states that the Mariana Trench is located in the Western Pacific Ocean, to the West of Mariana Island. This statement is not correct. The Mariana Trench is actually located to the east of the Mariana Islands. It stretches along the floor of the western Pacific Ocean and is situated in the western part of the Pacific Ring of Fire.

Option 2 mentions that the trench was first sounded during the Challenger expedition in 1875. This information is correct. The Challenger expedition, which took place from 1872 to 1876, was the first scientific oceanographic expedition. It conducted various studies, including the measurement of the depth of the Mariana Trench using a sounding device.

Option 3 states that the trench is about 2550 km long and has an average width of only 69 km. This is correct. The Mariana Trench is approximately 2,550 kilometers long and has an average width of about 69 kilometers. It is one of the longest and narrowest trenches on Earth.

Option 4 highlights that at the bottom of the trench, the water column exerts a pressure over 1000 times the standard atmospheric pressure at sea level. This statement is true. Due to the immense depth of the trench,