Daughter of uncle's father — Uncle's sister — Mother;

Mother's son — Brother 

Daughter of your father — Your sister. So, the person's mother is woman's sister or the woman is person's aunt. 

Fathometer is used to measure Ocean depth.

Fathometer is A depth finder that uses sound waves to determine the depth of water.

The Richter Scale is used to measure the intensity of Earthquakes.

The Decibel Scale is used to measure sound intensity.

The fruit content in both the fresh fruit and dry fruit is the same.

Given, fresh fruit has 68% water.so remaining 32% is fruit content. weight of fresh fruits is 100kg

Dry fruit has 20% water.so remaining 80% is fruit content.let weight if dry fruit be y kg.

Fruit % in freshfruit = Fruit% in dryfruit 

Therefore, (32/100) x 100 = (80/100 ) x y 

we get, y = 40 kg.

Seismography is an instrument to measure the intensity of an earthquake.

Similarly, taseometer is an instrument to measure strains.

Given Number:     4  2  1  5  7  9  3  6  8

Ascending order:  1  2  3  4  5  6  7  8  9

Hence the required pairs are  12, 49, 16

Modifier keys include Alt, Ctrl, Shift and the Windows key.

From all the hints given, 

only 042 satisfies and it unlocks the key.