Which one of the following is not a synthetic abrasive material

The flanks of teeth of rack-type gear cutter used for cutting involute gear profiles are:

The purpose of helical grooves in a twist drill is to
$$1.$$ Improve the stiffness
$$2.$$ Save a tool material
$$3.$$ Provide space for chip removal
$$4.$$ Provide rake angle for the cutting edge

Select the correct answer suing the codes given below

Tool life equation for two tools under consideration are as follows

$$\eqalign{ & HSS:\,\,\,\,\,\,\,\,\,\,\,\,\,V{T^{0.2}} = 150 \cr & Carbide:\,\,\,\,\,\,V{T^{0.3}} = 250 \cr} $$
Where $$V$$ is the cutting speed in $$m/min$$ and $$T$$ is the tool life in $$min.$$ The breakdown cutting speed above which the carbide tool will be beneficial is