How to use C# refelections to get properties that are instantiated or properties of a class type that are not null

I'm new to reflections, I want to know how to filter out the private properties and also get only the properties that are instantiated. Sample of what I would like to achieve is given below.

public class PersonalDetails
{
    internal Address AddressDetails { get; set; }
    public Contact ContactDetals { get; set; }

    public List<PersonalDetails> Friends { get; set; }        


    public string FirstName { get; set; }

    private int TempValue { get; set; }

    private int Id { get; set; }

    public PersonalDetails()
    {
        Id = 1;
        TempValue = 5;
    }
}

public class Address
{
    public string MailingAddress { get; set; }
    public string ResidentialAddress { get; set; }
}

public class Contact
{
    public string CellNumber { get; set; }

    public string OfficePhoneNumber { get; set; }
}

PersonalDetails pd = new PersonalDetails();
pd.FirstName = "First Name";
pd.ContactDetals = new Contact();
pd.ContactDetals.CellNumber = "666 666 666";

When I get the properties of object pd I want to filter out the properties that are private and not instantiated, like properties TempValue, Id and AddressDetails

Thanks in advance.