<PAGE>

                                                                   Exhibit 4.(b)

                                                           Executed in 6 Parts
                                                           Counterpart No. (   )


                              NATIONAL EQUITY TRUST

                        S&P 500 STRATEGY TRUST SERIES 16

                            REFERENCE TRUST AGREEMENT


         This Reference Trust Agreement dated January 30, 2002 among Prudential
Investment Management Services LLC, as Depositor, Prudential Securities
Incorporated, as Portfolio Supervisor, and The Bank of New York, as Trustee,
sets forth certain provisions in full and incorporates other provisions by
reference to the document entitled "National Equity Trust, Trust Indenture and
Agreement" (the "Basic Agreement") dated February 2, 2000. Such provisions as
are set forth in full herein and such provisions as are incorporated by
reference constitute a single instrument (the "Indenture").

                                WITNESSETH THAT:


         In consideration of the premises and of the mutual agreements herein
contained, the Depositor and the Trustee agree as follows:

                                     Part I.

                     STANDARD TERMS AND CONDITIONS OF TRUST


         Subject to the provisions of Part II hereof, all the provisions
contained in the Basic Agreement are herein incorporated by reference in their
entirety and shall be deemed to be a part of this instrument as fully and to the
same extent as though said provisions had been set forth in full in this
instrument.

         A. Article I, entitled "Definitions," shall be amended as follows:

         (i) Section 1.01-Definitions shall be amended to add the following
definition at the end thereof:


<PAGE>

                                      -2-


         "Portfolio Supervisor" of the Trust shall have the meaning assigned to
it in Part II of the Reference Trust Agreement.

         B. Article III, entitled "Administration of Trust," shall be amended as
follows:

         (i) The third paragraph of Section 3.05-Distribution shall be amended
by deleting any reference to Depositor and replacing it with Portfolio
Supervisor.

         (ii) Section 3.14-Deferred Sales Charge shall be amended to add the
following sentences at the end thereof:

         "References to Deferred Sales Charge in this Trust Indenture and
         Agreement shall include any Creation and Development Fee indicated in
         the prospectus for a Trust. The Creation and Development Fee shall be
         payable on each date so designated and in an amount determined as
         specified in the prospectus for a Trust."

         C. Article VIII, entitled "Depositor," shall be amended as follows:

         (i) Section 8.07-Compensation shall be amended by deleting any
reference to Depositor and replacing it with Portfolio Supervisor.

         D. Article IX, entitled "Additional Covenants; Miscellaneous
Provisions," shall be amended as follows:

         (i) The first sentence of Section 9.05 - Written Notice shall be
amended by deleting the language "Prudential Securities Incorporated at One
Seaport Plaza, New York, New York 10292" and replacing it with "Prudential
Investment Management LLC at 100 Mulberry Street, Gateway Center Three, Newark,
New Jersey 07102".

                                    Part II.

                      SPECIAL TERMS AND CONDITIONS OF TRUST

     The following special terms and conditions are hereby agreed to:

<PAGE>

                                      -3-

         A. The Trust is denominated National Equity Trust, S&P 500 Strategy
Trust Series 16.

         B. The Units of the Trust shall be subject to a deferred sales charge.

         C. The publicly traded stocks listed in Schedule A hereto are those
which, subject to the terms of this Indenture, have been or are to be deposited
in Trust under this Indenture as of the date hereof.

         D. The term "Depositor" shall mean Prudential Investment Management
Services LLC.

         E. The term "Portfolio Supervisor" shall mean Prudential Securities
Incorporated.

         F. The aggregate number of Units referred to in Sections 2.03 and 9.01
of the Basic Agreement is 125,000 as of the date hereof.

         G. A Unit of the Trust is hereby declared initially equal to
1/125,000th of the Trust.

         H. The term "First Settlement Date" shall mean February 5, 2002.

         I. The terms "Computation Day" and "Record Date" mean on the tenth day
of May 2002, August 2002, November 2002 and February 2003.

         J. The term "Distribution Date" shall mean on the twenty-fifth day of
May 2002, August 2002, November 2002 and February 2003.

         K. The term "Termination Date" shall mean March 4, 2003.

         L. The Trustee's Annual Fee shall be $.90 (per 1,000 Units) for
49,999,999 and below units outstanding $.84 (per 1,000 Units) on the next
50,000,000 Units, $.78 (per 1,000 Units) on the next 100,000,000 Units, and $.66
(per 1,000 Units) on Units in excess of 200,000,000 Units. In calculating the
Trustee's annual fee, the fee applicable to the number of units outstanding
shall apply to all units outstanding.

         M. The Portfolio Supervisor's portfolio supervisory service fee shall
be $.25 per 1,000 Units.

               [Signatures and acknowledgments on separate pages]


<PAGE>


                                      -4-

The Schedule of Portfolio Securities in Part A of the prospectus included in
this Registration Statement for National Equity Trust, S&P 500 Strategy Trust
Series 16 is hereby incorporated by reference herein as Schedule A hereto.