Q1: Minimum size of the particles of silt soil, is

ANS:A - 0.002 mm

I think the Silt varies(0.002-0.06) and the minimum is 0.002 and the maximum is 0.06.
So, it is correct. Clay= < 0.002.
Silt= 0.002 - 0.06.
Sand= 0.06 - 4.75.
Gravel=4.75+. Soil partial size;
clay: 0.002.
Silt: 0.002 - 0.06.
Sand: 0.06 - 4.75.
Gravel: 4.75 - 60.
Pebbels: 4.75 - 80. Size >300 mm - boulder.
Size ranges b/w 80 - 300 mm- cobbles.
Size ranges b/w 4.75 - 80 mm- gravel.
Size ranges b/w 75 micron - 4.75 mm - sand.
Size ranges b/w 0.002mm - 0.075mm - silt.
Size < 0.002 mm - clay soil. Clay- 0.002-2 micron

Silt - 2-75 micron
Fine - 2-10 micron
Medium - 10-20 micron
Course silt - 20-75 micron

Sand - 75 micron-4.75mm
Fine - 75 micron- 0.425mm
Medium - 0.425-2mm
Course sand - 2-4.75mm

Gravel - 4.75-80mm
Cobbels - 80-300mm
Boulders - >300mm