Ladle deoxidation of liquid steel is done at 1600°C by adding ferro-aluminium. By assuming Stokes law behaviour, time (in s) required for alumina particles of 50 μm diameter to float to the surface from a depth of 2 m would be
[Given: density of steel = 7000 kg/m³, density of alumina = 3650 kg/m³, viscosity of steel = 6 × 10^-3 kg/m/s]

Identify the incorrect statement with reference to L.D. steel making

A. The temperature of L.D. furnace is maintained at around 1600°C

B. The basicity of slag is maintained at around unity

C. Dephosphorisation and decarburisation should proceed simultaneously

D. High silicon hot metal may lead to sloping

The oxidising power of a steel making slag is dependent on the concentration of

A. CaO, because Ca²⁺ ions are oxidising to the elements

B. CaO, because O^2- ions are oxidising to the elements

C. FeO, because Fe²⁺ ions are oxidising to the elements

D. FeO, because O^2- ions are oxidising to the elements

Inclusion free steel are known as

A. Plain carbon steel

B. Clean steel

C. Alloy steel

D. None of these

Determine the correctness or otherwise of the following Assertion(a) and Reason(r):
Assertion (a): Deoxidation and decarburisation of liquid steel are done by vacuum treatment process.
Reason (r): Decreased partial pressure of CO(g) promotes deoxidation and decarburisation.

A. a is false but r is true

B. a is true but r is false

C. a is true and r is also true, but r is not the reason for a

D. a is true and r is also true, and r is the reason for a