Why is zero vector needed?

Fill in the blanks: A zero vector is represented by _____.

Let vecx, vecy and vecz be three vectors, each of magnitude sqrt2 and the angle between each pair of them is pi/3 . If veca is a non-zero vector perpendicular to vecx and vecy xx vecz and vecb is non-zero vector perpendicular to vecy and veczxxvecx , then :

If vec a is a non-zero vector of magnitude ‘a’ and λ a non-zero scalar, then λ vec a is unit vector if λ = - 1

If vec a is a non-zero vector of magnitude ‘a’ and λ a non-zero scalar, then λ vec a is unit vector if a = |λ|

If vec a is a non-zero vector of magnitude ‘a’ and λ a non-zero scalar, then λ vec a is unit vector if λ =1

If vec a is a non-zero vector of magnitude ‘a’ and λ a non-zero scalar, then λ vec a is unit vector if a = 1/ |λ|

If veca is a non-zero vector of modulus a and m is a non-zero scalar, then mveca is a unit vector if

Why is blood needed by all the parts of a body?