Yes, a vector which has zero magnitude is also a vector in case of two vectors travelling in opposite directions with equal magnitudes. At this case, the resultant vector has zero magnitude but it is still a vector. We call it a null vector.
It is theoretically possible for a substance to have a negative value of cubical expansivity, which means that the substance would contract rather than expand when the temperature increases. However, it is very rare for a substance to have a negative value of cubical expansivity over a significant range of temperatures.
One example of a substance that has a negative value of cubical expansivity over a limited range of temperatures is water. Water has a positive value of cubical expansivity at...
4.कमपयुटर हारडवेयर तिन परकारमा विभाजित छ। तिनीहरू हुन :
इनपुट उपकरण ( माउस, किबोरड, सकयानर)
आउटपुट उपकरण ( मनिटर, परिनटर, सपिकर)
परशोधन उपकरण (सि.पी. यु)
सोरेज उपकरण ( सिडि, पेन.डराइभ)
Sigma bond is stronger than Pi bond because of the following reasons:
- The extent of overlapping in Sigma bond is greater than in Pi bond.
- The electron density in intermolecular axis is more in Sigma bond than in Pi bond.
- There is free rotation of atom about Sigma bond but not about Pi bond.

Great my son!
You've been truly inspiration, dai! Congratulations to you and all of us.