Is the probability to raise kundalini with just applying the root lock high? Holding the breath and contracting the muscles down there after rapid breathing?

It is hardly likely that this will occur unless kundalini is first charged with the breath energy. Mere breathing in and out like a bellows (bhastrika = bellows in Sanskrit), will not cause kundalini to be charged unless somehow the infused energy goes to kundalini and charges it, or charges the sex organ chakra.

This implies that the yogi must push down the charged energy so that it does reach the base chakra, muladhar. The application of the root lock is for forcing the charge to remain there and accumulate, otherwise it might diffuse out from there and not build up to a charge.

Lightning occurs due to a buildup of static electricity in the air. If the static does not concentrate to a certain spot or zone, then it will be there but will not discharge in a powerful flash.

Question is that while you do rapid breathing, what do you do to be sure that the energy is actually going to muladhar chakra as its ultimate target. How do you compel the energy to build up there

In sex pleasure experience, the energy builds up in the sex organ chakra and then is released there in what is termed as a climax but that happens by the grace of nature with or without human impetus. Does the same thing happen in raising kundalini or is it that nature hardly helps and the person has to generate all of the impetus required?

~~~~~~~

Can kundalini be raised only in sitting and laying posture without doing any of the other postures?

Kundalini may itself rise without even one desiring it to do so, and it may do so from any posture or even from a damaged or critically wounded body. This can certainly happen.

Still, if something can happen, it may never happen all the same.