Select suitable characteristics of a primary standard?

P)Its composition should not change when  stored or during weighing

Q)It should have higher equivalent weight  so that percentage  error will be less

R)It should not decompose at ordinary temperature

S)It should be less soluble.

Primary  standard:       Primary standard is typically a reagent which can be

weighed easily, and which as so pure that its weight is truly representative

of the number of moles of substance contained

Features:         1) high purity  2) low reactivity          3) Low hygroscopicity

4)High equivalent wight

5)Non-toxicity 6)Ready and cheep  availability