It means that velocity not only has a size, but it also has a direction.
Some other vector quantities are force and acceleration.
They have sizes and directions.
Temperature, cost, and weight are quantities with only size and no direction.
Those are called "scalar" quantities.
Answer:
Study hard , focus on your studies and alyways ask questions .
Answer:B
Explanation:
Option A:
In the nuclear reactions,neutron can be split into proton an electron.
In this case,the number of protons are increasing,increasing the atomic number.
Hence,the atomic number is not conserved.
Option B:
In any reaction the sum of number of neutrons and number of protons remain constant before and after the reaction.
Option C:
The mass number may change for the atoms.For example
emission reduces the atomic number by 
Option D:
In the nuclear reactions,neutron can be split into proton an electron.
So,they number of neutrons may change.
Blacklight is made of a type of ultraviolet light called UV-A, but blacklight is not the same as ultraviolet light. Blacklight lamps only emit in the lower energy range of ultraviolet light.